/* Loading Screen Styles */
.loading-screen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    z-index: 9999;
    color: white;
    font-family: 'Poppins', sans-serif;
    transition: opacity 0.5s ease-out, visibility 0.5s ease-out;
}

.loading-screen.hidden {
    opacity: 0;
    visibility: hidden;
}

.loading-spinner {
    width: 50px;
    height: 50px;
    border: 4px solid rgba(255, 255, 255, 0.3);
    border-top: 4px solid white;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-bottom: 20px;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

.loading-screen p {
    font-size: 18px;
    font-weight: 500;
    margin: 0;
    opacity: 0.9;
}

/* Enhanced Study Platform Styles */

/* Mobile Search Styles */
.mobile-search {
    display: none;
    width: 100%;
    padding: 12px 16px;
    background: var(--bg-card);
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 60px;
    z-index: 100;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.mobile-search .search {
    width: 100%;
    max-width: 100%;
    padding: 12px 16px;
    border-radius: 12px;
    border: 1px solid var(--border);
    background: var(--bg-subtle);
    color: var(--text);
    font-size: 14px;
    transition: all 0.3s ease;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
}

.mobile-search .search:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 2px rgba(var(--primary-rgb), 0.2);
    outline: none;
}

.mobile-search.hidden {
    display: none;
}

@media (max-width: 768px) {
    .mobile-search {
        display: block;
    }
    
    .nav-center {
        display: none;
    }
}

/* Main Layout */
.study-main {
    display: grid;
    grid-template-columns: 320px 1fr;
    gap: 32px;
    min-height: calc(100vh - 80px);
    background: var(--bg);
    padding: 24px;
    max-width: 1400px;
    margin: 0 auto;
}

@media (max-width: 1024px) {
    .study-main {
        padding: 20px;
        gap: 24px;
    }
}

@media (max-width: 768px) {
    .study-main {
        grid-template-columns: 1fr;
        padding: 16px;
        gap: 20px;
        margin-top: 10px;
    }
    
    .nav-center .search {
        display: none;
    }
}

@media (max-width: 480px) {
    .study-main {
        padding: 12px;
        gap: 16px;
    }
}

/* Subject Selector - Enhanced with gradient and glass effect */
.subject-selector {
    grid-column: 1 / -1;
    background: linear-gradient(135deg, var(--primary-color) 0%, rgba(99, 102, 241, 0.8) 100%);
    border-radius: 24px;
    padding: 32px;
    margin-bottom: 32px;
    box-shadow: 0 20px 40px rgba(99, 102, 241, 0.15);
    border: 1px solid rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(20px);
    position: relative;
    overflow: hidden;
}

.subject-selector::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(45deg, transparent 30%, rgba(255, 255, 255, 0.1) 50%, transparent 70%);
    animation: shimmer 3s infinite;
    pointer-events: none;
}

.subject-tabs {
    display: flex;
    gap: 16px;
    justify-content: center;
    flex-wrap: wrap;
    position: relative;
    z-index: 1;
}

.subject-tab {
    background: rgba(255, 255, 255, 0.15);
    border: 2px solid rgba(255, 255, 255, 0.25);
    color: white;
    padding: 16px 28px;
    border-radius: 16px;
    font-weight: 700;
    font-size: 15px;
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    gap: 10px;
    min-width: 150px;
    justify-content: center;
    backdrop-filter: blur(10px);
    position: relative;
    overflow: hidden;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.subject-tab::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.3), transparent);
    transition: left 0.6s;
}

.subject-tab:hover::before {
    left: 100%;
}

.subject-tab:hover {
    background: rgba(255, 255, 255, 0.3);
    border-color: rgba(255, 255, 255, 0.6);
    transform: translateY(-3px) scale(1.02);
    box-shadow: 0 12px 28px rgba(0, 0, 0, 0.15);
    color: white;
}

.subject-tab.active {
    background: linear-gradient(135deg, rgba(0, 115, 255, 0.95), rgba(0, 4, 255, 0.85));
    border-color: white;
    color: var(--primary-color);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
    transform: translateY(-2px);
}

.subject-tab.active:hover {
    background: linear-gradient(135deg, rgba(255, 255, 255, 1), rgba(255, 255, 255, 0.95));
    color: var(--primary-color);
    transform: translateY(-3px) scale(1.02);
    box-shadow: 0 12px 32px rgba(0, 0, 0, 0.25);
}

/* Light theme specific overrides */
:root:not(.dark) .subject-tab {
    background: rgb(255, 255, 255);
    border: 2px solid rgba(99, 102, 241, 0.2);
    color: var(--primary-color);
}

:root:not(.dark) .subject-tab:hover {
    background: rgba(99, 102, 241, 0.15);
    border-color: rgba(99, 102, 241, 0.4);
    color: var(--primary-color);
    box-shadow: 0 12px 28px rgba(99, 102, 241, 0.2);
}

:root:not(.dark) .subject-tab.active {
    background: linear-gradient(135deg, var(--primary-color), rgba(99, 102, 241, 0.9));
    border-color: var(--primary-color);
    color: rgb(0, 0, 0);
    box-shadow: 0 8px 24px rgba(99, 102, 241, 0.3);
}

:root:not(.dark) .subject-tab.active:hover {
    background: linear-gradient(135deg, rgba(99, 102, 241, 1.1), var(--primary-color));
    color: rgb(0, 0, 0);
    box-shadow: 0 12px 32px rgba(99, 102, 241, 0.4);
}

/* Study Navigation - Enhanced sidebar */
.study-nav {
    background: var(--bg-card);
    border-radius: 24px;
    padding: 28px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.08);
    border: 1px solid var(--border);
    height: fit-content;
    position: sticky;
    top: 24px;
    backdrop-filter: blur(20px);
}

.nav-header {
    margin-bottom: 28px;
    padding-bottom: 24px;
    border-bottom: 2px solid var(--border);
    position: relative;
}

.nav-header::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    width: 60px;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-color), var(--primary-dark));
    border-radius: 2px;
}

.nav-header h2 {
    margin: 0 0 12px;
    font-size: 22px;
    font-weight: 800;
    background: linear-gradient(135deg, var(--text), var(--primary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    line-height: 1.2;
}

.progress-indicator {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
    color: var(--text-secondary);
    background: var(--bg-elev);
    padding: 10px 16px;
    border-radius: 12px;
    font-weight: 600;
    border: 1px solid var(--border);
}

.chapter-list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.chapter-item {
    background: var(--bg-elev);
    border: 2px solid transparent;
    border-radius: 20px;
    padding: 20px;
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
    backdrop-filter: blur(10px);
}

.chapter-item::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    width: 5px;
    height: 100%;
    background: linear-gradient(180deg, var(--primary-color), var(--primary-dark));
    transform: scaleY(0);
    transition: transform 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    transform-origin: bottom;
    border-radius: 0 5px 5px 0;
}

.chapter-item::after {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(var(--primary-rgb, 99, 102, 241), 0.1), transparent);
    transition: left 0.6s;
}

.chapter-item:hover::before {
    transform: scaleY(1);
}

.chapter-item:hover::after {
    left: 100%;
}

.chapter-item:hover {
    transform: translateX(8px);
    border-color: var(--primary-color);
    box-shadow: 0 8px 32px rgba(var(--primary-rgb, 99, 102, 241), 0.2);
    background: var(--bg-card);
}

.chapter-item.active {
    border-color: var(--primary-color);
    background: var(--primary-light);
    transform: translateX(12px);
    box-shadow: 0 12px 40px rgba(var(--primary-rgb, 99, 102, 241), 0.3);
}

.chapter-item.active::before {
    transform: scaleY(1);
}

.chapter-item.completed {
    background: var(--success-light);
    border-color: var(--success);
}

.chapter-item.completed:hover {
    background: var(--success);
    color: white;
}

.chapter-item h3 {
    font-size: 17px;
    font-weight: 700;
    margin-bottom: 8px;
    line-height: 1.3;
    color: var(--text);
}

/* Light theme specific chapter item styles */
:root:not(.dark) .chapter-item.active h3 {
    color: var(--primary-color);
    font-weight: 800;
}

:root:not(.dark) .chapter-item.active {
    background: rgba(99, 102, 241, 0.1);
    border-color: var(--primary-color);
    color: var(--primary-color);
}

.chapter-item p {
    font-size: 13px;
    opacity: 0.8;
    margin-bottom: 12px;
    color: var(--text-secondary);
}

.status-badge {
    display: inline-block;
    padding: 6px 12px;
    border-radius: 12px;
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.status-badge.completed {
    background: var(--success);
    color: white;
}

.status-badge.pending {
    background: var(--warning-light);
    color: var(--warning-dark);
}

/* Study Content - Enhanced main content area */
.study-content {
    background: var(--bg-card);
    border-radius: 24px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.08);
    border: 1px solid var(--border);
    overflow: hidden;
    backdrop-filter: blur(20px);
}

.content-header {
    background: linear-gradient(135deg, var(--bg-elev) 0%, var(--bg-card) 100%);
    padding: 36px;
    border-bottom: 2px solid var(--border);
    position: relative;
}

.content-header::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 36px;
    right: 36px;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-color), transparent);
}

.content-header h1 {
    font-size: 32px;
    font-weight: 800;
    color: var(--text);
    margin-bottom: 24px;
    line-height: 1.2;
    background: linear-gradient(135deg, var(--text), var(--primary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* Light theme specific content header styles */
:root:not(.dark) .content-header h1 {
    background: linear-gradient(135deg, var(--primary-color), rgba(99, 102, 241, 0.8));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.content-tabs {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

.tab-btn {
    background: transparent;
    border: 2px solid var(--border);
    border-radius: 16px;
    padding: 14px 24px;
    font-size: 15px;
    font-weight: 700;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    gap: 8px;
    position: relative;
    overflow: hidden;
}

.tab-btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(var(--primary-rgb, 99, 102, 241), 0.1), transparent);
    transition: left 0.5s;
}

.tab-btn:hover::before {
    left: 100%;
}

.tab-btn:hover {
    background: var(--primary-light);
    border-color: var(--primary-color);
    color: var(--primary-color);
    transform: translateY(-3px);
    box-shadow: 0 8px 24px rgba(var(--primary-rgb, 99, 102, 241), 0.2);
}

.tab-btn.active {
    background: var(--primary-color);
    border-color: var(--primary-color);
    color: white;
    box-shadow: 0 6px 20px rgba(var(--primary-rgb, 99, 102, 241), 0.4);
    transform: translateY(-2px);
}

/* Light theme specific tab button styles */
:root:not(.dark) .tab-btn {
    background: rgba(99, 102, 241, 0.05);
    border: 2px solid rgba(99, 102, 241, 0.15);
    color: var(--primary-color);
}

:root:not(.dark) .tab-btn:hover {
    background: rgba(99, 102, 241, 0.1);
    border-color: rgba(99, 102, 241, 0.3);
    color: var(--primary-color);
    transform: translateY(-3px);
    box-shadow: 0 8px 24px rgba(99, 102, 241, 0.2);
}

:root:not(.dark) .tab-btn.active {
    background: var(--primary-color);
    border-color: var(--primary-color);
    color: rgb(0, 0, 0);
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.4);
    transform: translateY(-2px);
}

.tab-content {
    padding: 36px;
}

.tab-panel {
    display: none;
}

.tab-panel.active {
    display: block;
    animation: fadeInUp 0.5s ease-out;
}

/* Welcome Message - Enhanced with animations */
.welcome-message {
    text-align: center;
    padding: 80px 40px;
    background: linear-gradient(135deg, var(--primary-color) 0%, rgba(139, 92, 246, 0.9) 100%);
    border-radius: 24px;
    color: white;
    margin-bottom: 32px;
    position: relative;
    overflow: hidden;
    box-shadow: 0 20px 60px rgba(99, 102, 241, 0.3);
}

.welcome-message::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(45deg, transparent 30%, rgba(255, 255, 255, 0.1) 50%, transparent 70%);
    animation: shimmer 4s infinite;
    pointer-events: none;
}

.welcome-icon {
    font-size: 80px;
    margin-bottom: 28px;
    animation: float 3s ease-in-out infinite;
    position: relative;
    z-index: 1;
}

.welcome-message h2 {
    font-size: 36px;
    font-weight: 800;
    margin-bottom: 20px;
    position: relative;
    z-index: 1;
}

.welcome-message p {
    font-size: 18px;
    opacity: 0.95;
    margin-bottom: 40px;
    line-height: 1.7;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
    position: relative;
    z-index: 1;
}

.study-features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 24px;
    margin-top: 40px;
    position: relative;
    z-index: 1;
}

.feature-item {
    background: rgba(255, 255, 255, 0.15);
    border-radius: 20px;
    padding: 24px;
    display: flex;
    align-items: center;
    gap: 16px;
    backdrop-filter: blur(15px);
    border: 1px solid rgba(255, 255, 255, 0.25);
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.feature-item:hover {
    transform: translateY(-5px);
    background: rgba(255, 255, 255, 0.2);
    box-shadow: 0 12px 32px rgba(0, 0, 0, 0.2);
}

.feature-icon {
    font-size: 28px;
    flex-shrink: 0;
}

/* Chapter Content - Enhanced styling */
.chapter-content {
    max-width: 100%;
}

.chapter-header-actions {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 32px;
    padding: 28px;
    background: var(--bg-elev);
    border-radius: 20px;
    border: 2px solid var(--border);
    backdrop-filter: blur(10px);
}

.chapter-meta {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
}

.weightage-badge {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: rgb(0, 255, 106);
    padding: 10px 20px;
    border-radius: 16px;
    font-size: 14px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    box-shadow: 0 4px 12px rgba(var(--primary-rgb, 99, 102, 241), 0.3);
}

.questions-count {
    background: linear-gradient(135deg, var(--success), #10b981);
    color: white;
    padding: 10px 20px;
    border-radius: 16px;
    font-size: 14px;
    font-weight: 700;
    box-shadow: 0 4px 12px rgba(34, 197, 94, 0.3);
}

.completion-btn {
    padding: 14px 28px;
    border-radius: 16px;
    font-weight: 700;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.completion-btn:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
}

/* MAXIMUM SPECIFICITY COMPLETION BUTTON STYLES FOR LIGHT THEME */
/* Target the exact button structure from JavaScript: btn + (success|primary) + completion-btn */

/* Primary state completion button */
:root:not(.dark) button#toggle-completion.btn.primary.completion-btn,
:root:not(.dark) .btn.primary.completion-btn,
:root:not(.dark) button.btn.primary.completion-btn,
:root:not(.dark) .chapter-header-actions button.btn.primary.completion-btn,
:root:not(.dark) .chapter-header-actions .btn.primary.completion-btn,
:root:not(.dark) .study-content button.btn.primary.completion-btn,
:root:not(.dark) .study-content .btn.primary.completion-btn,
:root:not(.dark) .tab-content button.btn.primary.completion-btn,
:root:not(.dark) .tab-content .btn.primary.completion-btn {
    background: #6366f1 !important;
    background-color: #6366f1 !important;
    border: 2px solid #6366f1 !important;
    border-color: #6366f1 !important;
    color: #ffffff !important;
    -webkit-text-fill-color: #ffffff !important;
    text-shadow: none !important;
    opacity: 1 !important;
    font-weight: 700 !important;
}

:root:not(.dark) button#toggle-completion.btn.primary.completion-btn:hover,
:root:not(.dark) .btn.primary.completion-btn:hover,
:root:not(.dark) button.btn.primary.completion-btn:hover,
:root:not(.dark) .chapter-header-actions button.btn.primary.completion-btn:hover,
:root:not(.dark) .chapter-header-actions .btn.primary.completion-btn:hover,
:root:not(.dark) .study-content button.btn.primary.completion-btn:hover,
:root:not(.dark) .study-content .btn.primary.completion-btn:hover,
:root:not(.dark) .tab-content button.btn.primary.completion-btn:hover,
:root:not(.dark) .tab-content .btn.primary.completion-btn:hover {
    background: rgba(99, 102, 241, 0.9) !important;
    background-color: rgba(99, 102, 241, 0.9) !important;
    border-color: #6366f1 !important;
    color: #ffffff !important;
    -webkit-text-fill-color: #ffffff !important;
    text-shadow: none !important;
    opacity: 1 !important;
    box-shadow: 0 8px 24px rgba(99, 102, 241, 0.3) !important;
}

/* Success state completion button */
:root:not(.dark) button#toggle-completion.btn.success.completion-btn,
:root:not(.dark) .btn.success.completion-btn,
:root:not(.dark) button.btn.success.completion-btn,
:root:not(.dark) .chapter-header-actions button.btn.success.completion-btn,
:root:not(.dark) .chapter-header-actions .btn.success.completion-btn,
:root:not(.dark) .study-content button.btn.success.completion-btn,
:root:not(.dark) .study-content .btn.success.completion-btn,
:root:not(.dark) .tab-content button.btn.success.completion-btn,
:root:not(.dark) .tab-content .btn.success.completion-btn {
    background: #10b981 !important;
    background-color: #10b981 !important;
    border: 2px solid #10b981 !important;
    border-color: #10b981 !important;
    color: #ffffff !important;
    -webkit-text-fill-color: #ffffff !important;
    text-shadow: none !important;
    opacity: 1 !important;
    font-weight: 700 !important;
}

:root:not(.dark) button#toggle-completion.btn.success.completion-btn:hover,
:root:not(.dark) .btn.success.completion-btn:hover,
:root:not(.dark) button.btn.success.completion-btn:hover,
:root:not(.dark) .chapter-header-actions button.btn.success.completion-btn:hover,
:root:not(.dark) .chapter-header-actions .btn.success.completion-btn:hover,
:root:not(.dark) .study-content button.btn.success.completion-btn:hover,
:root:not(.dark) .study-content .btn.success.completion-btn:hover,
:root:not(.dark) .tab-content button.btn.success.completion-btn:hover,
:root:not(.dark) .tab-content .btn.success.completion-btn:hover {
    background: rgba(16, 185, 129, 0.9) !important;
    background-color: rgba(16, 185, 129, 0.9) !important;
    border-color: #10b981 !important;
    color: #ffffff !important;
    -webkit-text-fill-color: #ffffff !important;
    text-shadow: none !important;
    opacity: 1 !important;
    box-shadow: 0 8px 24px rgba(16, 185, 129, 0.3) !important;
}

/* Fallback for any completion-btn class */
:root:not(.dark) .completion-btn,
:root:not(.dark) button.completion-btn,
:root:not(.dark) .btn.completion-btn {
    background: #6366f1 !important;
    background-color: #6366f1 !important;
    border: 2px solid #6366f1 !important;
    border-color: #6366f1 !important;
    color: #ffffff !important;
    -webkit-text-fill-color: #ffffff !important;
    text-shadow: none !important;
    opacity: 1 !important;
    font-weight: 700 !important;
}

:root:not(.dark) .completion-btn:hover,
:root:not(.dark) button.completion-btn:hover,
:root:not(.dark) .btn.completion-btn:hover {
    background: rgba(99, 102, 241, 0.9) !important;
    background-color: rgba(99, 102, 241, 0.9) !important;
    border-color: #6366f1 !important;
    color: #ffffff !important;
    -webkit-text-fill-color: #ffffff !important;
    text-shadow: none !important;
    opacity: 1 !important;
    box-shadow: 0 8px 24px rgba(99, 102, 241, 0.3) !important;
}

/* Light theme specific button styles */
:root:not(.dark) .btn.primary {
    background: var(--primary-color);
    border: 2px solid var(--primary-color);
    color: white;
}

:root:not(.dark) .btn.primary:hover {
    background: rgba(99, 102, 241, 0.9);
    border-color: rgba(99, 102, 241, 0.9);
    color: white;
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.3);
}

:root:not(.dark) .btn.success {
    background: var(--success);
    border: 2px solid var(--success);
    color: white;
}

:root:not(.dark) .btn.success:hover {
    background: rgba(34, 197, 94, 0.9);
    border-color: rgba(34, 197, 94, 0.9);
    color: white;
    box-shadow: 0 6px 20px rgba(34, 197, 94, 0.3);
}

:root:not(.dark) .btn.secondary {
    background: rgba(99, 102, 241, 0.1);
    border: 2px solid rgba(99, 102, 241, 0.2);
    color: var(--primary-color);
}

:root:not(.dark) .btn.secondary:hover {
    background: rgba(99, 102, 241, 0.15);
    border-color: rgba(99, 102, 241, 0.3);
    color: var(--primary-color);
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.2);
}

.chapter-intro {
    margin-bottom: 36px;
    padding: 32px;
    background: var(--bg-card);
    border-radius: 20px;
    border-left: 5px solid var(--primary-color);
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
    position: relative;
    overflow: hidden;
}

.chapter-intro::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 5px;
    height: 100%;
    background: linear-gradient(180deg, var(--primary-color), var(--primary-dark));
}

.chapter-intro h2 {
    font-size: 28px;
    font-weight: 800;
    color: var(--text);
    margin-bottom: 20px;
}

.chapter-intro p {
    font-size: 17px;
    line-height: 1.8;
    color: var(--text-secondary);
}

.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 28px;
}

.topic-card {
    background: var(--bg-card);
    border: 2px solid var(--border);
    border-radius: 20px;
    padding: 28px;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
}

.topic-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(var(--primary-rgb, 99, 102, 241), 0.05), transparent);
    transition: left 0.6s;
}

.topic-card:hover::before {
    left: 100%;
}

.topic-card:hover {
    border-color: var(--primary-color);
    transform: translateY(-6px);
    box-shadow: 0 12px 40px rgba(var(--primary-rgb, 99, 102, 241), 0.15);
}

.topic-card h3 {
    font-size: 20px;
    font-weight: 700;
    color: var(--text);
    margin-bottom: 16px;
}

.topic-card p {
    font-size: 15px;
    line-height: 1.7;
    color: var(--text-secondary);
}

/* Subtopics Section Styles */
.subtopics-section {
    margin-top: 24px;
    padding-top: 20px;
    border-top: 2px solid var(--border);
}

.subtopic-item {
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 16px;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.subtopic-item::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    width: 4px;
    height: 100%;
    background: linear-gradient(180deg, var(--primary-color), var(--primary-dark));
    transform: scaleY(0);
    transition: transform 0.3s ease;
    transform-origin: bottom;
}

.subtopic-item:hover::before {
    transform: scaleY(1);
}

.subtopic-item:hover {
    border-color: var(--primary-color);
    background: var(--bg-card);
    transform: translateX(4px);
    box-shadow: 0 4px 16px rgba(var(--primary-rgb, 99, 102, 241), 0.1);
}

.subtopic-item h4 {
    font-size: 16px;
    font-weight: 700;
    color: var(--text);
    margin-bottom: 12px;
    line-height: 1.3;
}

.subtopic-explanation {
    font-size: 14px;
    line-height: 1.7;
    color: var(--text-secondary);
    margin: 0;
}

/* Light theme specific subtopic styles */
:root:not(.dark) .subtopics-section {
    border-top-color: rgba(99, 102, 241, 0.2);
}

:root:not(.dark) .subtopic-item {
    background: rgba(99, 102, 241, 0.05);
    border-color: rgba(99, 102, 241, 0.15);
}

:root:not(.dark) .subtopic-item:hover {
    background: rgba(99, 102, 241, 0.1);
    border-color: rgba(99, 102, 241, 0.3);
    box-shadow: 0 4px 16px rgba(99, 102, 241, 0.15);
}

:root:not(.dark) .subtopic-item h4 {
    color: var(--primary-color);
}

/* Enhanced Animations */
@keyframes float {
    0%, 100% { 
        transform: translateY(0px) rotate(0deg); 
    }
    33% { 
        transform: translateY(-10px) rotate(1deg); 
    }
    66% { 
        transform: translateY(-5px) rotate(-1deg); 
    }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes shimmer {
    0% { 
        background-position: -200% 0; 
    }
    100% { 
        background-position: 200% 0; 
    }
}

/* Completion functionality styles */
.completion-message {
    position: fixed;
    top: 24px;
    right: 24px;
    z-index: 1000;
    opacity: 0;
    transform: translateX(100%);
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.completion-message.show {
    opacity: 1;
    transform: translateX(0);
}

.completion-content {
    background: linear-gradient(135deg, var(--success), #10b981);
    color: white;
    padding: 20px 24px;
    border-radius: 16px;
    display: flex;
    align-items: center;
    gap: 16px;
    box-shadow: 0 8px 32px rgba(34, 197, 94, 0.3);
    min-width: 320px;
    backdrop-filter: blur(20px);
}

.completion-icon {
    font-size: 24px;
}

.completion-text {
    font-weight: 600;
    font-size: 15px;
}

/* Auto-completion message styles */
.completion-message.auto-completion .completion-content {
    background: linear-gradient(135deg, #8b5cf6, #a855f7);
    box-shadow: 0 8px 32px rgba(139, 92, 246, 0.4);
    flex-direction: column;
    align-items: flex-start;
    min-width: 380px;
    padding: 24px 28px;
}

.completion-message.auto-completion .completion-details {
    font-size: 13px;
    opacity: 0.9;
    margin-top: 8px;
    font-weight: 500;
}

/* Progress tracker styles */
.progress-tracker {
    display: flex;
    flex-direction: column;
    gap: 12px;
    background: var(--bg-elev);
    border: 2px solid var(--border);
    border-radius: 16px;
    padding: 20px;
    backdrop-filter: blur(10px);
}

.progress-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 16px;
    background: var(--bg-card);
    border: 2px solid var(--border);
    border-radius: 12px;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    font-weight: 600;
    font-size: 14px;
    color: var(--text-secondary);
}

.progress-item.completed {
    border-color: var(--success);
    background: var(--success-light);
    color: var(--success);
    transform: scale(1.02);
}

.progress-item.completed .progress-icon {
    animation: bounce 0.6s ease-out;
}

.progress-icon {
    font-size: 18px;
    flex-shrink: 0;
}

.completion-status {
    display: flex;
    align-items: center;
    gap: 12px;
}

.completion-indicator {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 12px 20px;
    border-radius: 12px;
    font-weight: 700;
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    background: var(--success);
    color: white;
    border: 2px solid var(--success);
    box-shadow: 0 4px 16px rgba(34, 197, 94, 0.3);
    animation: completionPulse 2s ease-out;
}

@keyframes bounce {
    0%, 20%, 53%, 80%, 100% {
        transform: translate3d(0,0,0);
    }
    40%, 43% {
        transform: translate3d(0, -8px, 0);
    }
    70% {
        transform: translate3d(0, -4px, 0);
    }
    90% {
        transform: translate3d(0, -2px, 0);
    }
}

@keyframes completionPulse {
    0% {
        transform: scale(1);
        box-shadow: 0 4px 16px rgba(34, 197, 94, 0.3);
    }
    50% {
        transform: scale(1.05);
        box-shadow: 0 8px 24px rgba(34, 197, 94, 0.5);
    }
    100% {
        transform: scale(1);
        box-shadow: 0 4px 16px rgba(34, 197, 94, 0.3);
    }
}

/* Light theme specific progress tracker styles */
:root:not(.dark) .progress-tracker {
    background: rgba(99, 102, 241, 0.05);
    border-color: rgba(99, 102, 241, 0.15);
}

:root:not(.dark) .progress-item {
    background: rgba(255, 255, 255, 0.8);
    border-color: rgba(99, 102, 241, 0.2);
    color: var(--primary-color);
}

:root:not(.dark) .progress-item.completed {
    background: rgba(34, 197, 94, 0.1);
    border-color: var(--success);
    color: var(--success);
}

:root:not(.dark) .completion-indicator {
    background: var(--success);
    border-color: var(--success);
    color: white;
}

/* Enhanced Quiz Styles */
.quiz-container {
    max-width: 900px;
    margin: 0 auto;
}

.quiz-header {
    text-align: center;
    margin-bottom: 36px;
    padding: 32px;
    background: linear-gradient(135deg, var(--bg-elev) 0%, var(--bg-card) 100%);
    border-radius: 24px;
    border: 2px solid var(--border);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.08);
}

.question-card {
    background: var(--bg-card);
    border: 2px solid var(--border);
    border-radius: 20px;
    padding: 32px;
    margin-bottom: 28px;
    box-shadow: 0 6px 24px rgba(0, 0, 0, 0.08);
    transition: all 0.3s ease;
}

.question-card:hover {
    box-shadow: 0 12px 40px rgba(0, 0, 0, 0.12);
    transform: translateY(-2px);
}

.options-list {
    display: grid;
    gap: 16px;
    margin-bottom: 24px;
}

.option-item {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 16px 20px;
    background: var(--bg-elev);
    border: 2px solid var(--border);
    border-radius: 16px;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    font-weight: 500;
}

.option-item:hover {
    border-color: var(--primary-color);
    background: var(--bg-card);
    transform: translateX(4px);
}

.option-item.selected {
    border-color: var(--primary-color);
    background: var(--primary-light);
    color: var(--primary-color);
    transform: translateX(8px);
}

/* Responsive Design */
@media (max-width: 1200px) {
    .study-main {
        grid-template-columns: 280px 1fr;
        gap: 24px;
        padding: 20px;
    }
}

@media (max-width: 968px) {
    .study-main {
        grid-template-columns: 1fr;
        gap: 24px;
        padding: 16px;
        display: flex;
        flex-direction: column;
    }
    
    .study-nav {
        position: static;
        order: 1;
        max-height: 60vh;
        overflow-y: auto;
        background: var(--bg-elev);
        border: 1px solid var(--border);
        border-radius: var(--radius-lg);
        margin-bottom: 20px;
    }
    
    .study-content {
        order: 2;
    }
    
    .subject-selector {
        padding: 28px;
        order: 0;
    }
    
    .content-header {
        padding: 28px;
    }
    
    .content-header h1 {
        font-size: 28px;
    }
    
    .tab-content {
        padding: 28px;
    }
     .signup-btn{
        width: 100%;
        max-width: 280px;
        padding: 14px 24px;
        font-size: 15px;
    }
}

@media (max-width: 768px) {
    .study-main {
        padding: 12px;
        display: flex;
        flex-direction: column;
    }
    
    .subject-selector {
        padding: 24px;
        margin-bottom: 24px;
        order: 0;
    }
    
    .study-nav {
        order: 1;
        max-height: 50vh;
        overflow-y: auto;
        background: var(--bg-elev);
        border: 1px solid var(--border);
        border-radius: var(--radius-lg);
        margin-bottom: 20px;
        scrollbar-width: thin;
        scrollbar-color: var(--primary) var(--bg-elev);
    }
    
    .study-nav::-webkit-scrollbar {
        width: 6px;
    }
    
    .study-nav::-webkit-scrollbar-track {
        background: var(--bg-elev);
        border-radius: 3px;
    }
    
    .study-nav::-webkit-scrollbar-thumb {
        background: var(--primary);
        border-radius: 3px;
    }
    
    .study-content {
        order: 2;
    }
    
    .subject-tabs {
        gap: 12px;
    }
    
    .subject-tab {
        padding: 14px 20px;
        font-size: 14px;
        min-width: 130px;
    }
    
    .chapter-header-actions {
        flex-direction: column;
        gap: 20px;
        align-items: center;
        padding: 24px;
    }
    
    .chapter-meta {
        justify-content: center;
    }
    
    .topics-grid {
        grid-template-columns: 1fr;
        gap: 20px;
    }
    
    .welcome-message {
        padding: 60px 28px;
    }
    
    .welcome-message h2 {
        font-size: 28px;
    }
    
    .welcome-message p {
        font-size: 16px;
    }
    
    .study-features {
        grid-template-columns: 1fr;
        gap: 16px;
    }
    
    .content-header {
        padding: 24px;
    }
    
    .tab-content {
        padding: 24px;
    }
    .signup-btn:hover{
        width: 100%;
        max-width: 280px;
        padding: 14px 24px;
        font-size: 15px;
    }
}

@media (max-width: 480px) {
    .study-main {
        padding: 8px;
        gap: 16px;
        display: flex;
        flex-direction: column;
    }
    
    .subject-selector {
        padding: 20px;
        margin-bottom: 16px;
        order: 0;
    }
    
    .study-nav {
        order: 1;
        max-height: 45vh;
        margin-bottom: 16px;
        padding: 20px;
        background: var(--bg-elev);
        border: 1px solid var(--border);
        border-radius: var(--radius);
    }
    
    .nav-header h2 {
        font-size: 18px;
        margin-bottom: 16px;
    }
    
    .chapter-list {
        gap: 12px;
    }
    
    .chapter-item {
        padding: 14px;
        border-radius: var(--radius);
        cursor: pointer;
        -webkit-tap-highlight-color: transparent;
        touch-action: manipulation;
    }
    
    .chapter-item:active {
        transform: scale(0.98);
        transition: transform 0.1s ease;
    }
    
    .chapter-item h3 {
        font-size: 15px;
        margin-bottom: 6px;
    }
    
    .chapter-item p {
        font-size: 12px;
        margin-bottom: 8px;
    }
    
    .study-content {
        order: 2;
    }
    
    .subject-tabs {
        flex-direction: column;
        gap: 8px;
    }
    
    .subject-tab {
        width: 100%;
        min-width: unset;
        padding: 12px 16px;
        font-size: 13px;
    }
    
    .content-tabs {
        flex-direction: column;
        gap: 8px;
    }
    
    .tab-btn {
        width: 100%;
        justify-content: center;
        padding: 12px 20px;
        font-size: 14px;
    }
    
    .content-header {
        padding: 20px;
    }
    
    .content-header h1 {
        font-size: 24px;
    }
    
    .tab-content {
        padding: 20px;
    }
    
    .welcome-icon {
        font-size: 60px;
    }
    
    .welcome-message h2 {
        font-size: 24px;
    }
    
    .welcome-message p {
        font-size: 15px;
    }
    
    .welcome-message {
        padding: 40px 20px;
    }
    
    .completion-message {
        right: 12px;
        left: 12px;
    }
    
    .completion-content {
        min-width: auto;
    }
}

/* Dark mode enhancements */
:root.dark .subject-selector {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.3) 0%, rgba(139, 92, 246, 0.2) 100%);
    border-color: rgba(99, 102, 241, 0.4);
}

:root.dark .welcome-message {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.4) 0%, rgba(139, 92, 246, 0.3) 100%);
}

:root.dark .feature-item {
    background: rgba(255, 255, 255, 0.05);
    border-color: rgba(255, 255, 255, 0.1);
}

/* Focus states for accessibility */
.subject-tab:focus,
.tab-btn:focus,
.chapter-item:focus,
.completion-btn:focus,
.option-item:focus {
    outline: 3px solid var(--primary-color);
    outline-offset: 2px;
}

/* Smooth transitions for all interactive elements */
* {
    transition: background-color 0.3s ease, border-color 0.3s ease, color 0.3s ease, transform 0.3s ease, box-shadow 0.3s ease;
}

/* Additional Quiz and Formula Styles from original */
.formulas-section {
    display: grid;
    gap: 24px;
}

.formula-category {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    padding: 28px;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
}

.formula-category h3 {
    margin: 0 0 20px;
    font-size: 22px;
    font-weight: 700;
    color: var(--text);
    padding-bottom: 16px;
    border-bottom: 2px solid var(--border);
}

.formula-list {
    display: grid;
    gap: 16px;
}

.formula-item {
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 20px;
    transition: all 0.3s ease;
}

.formula-item:hover {
    border-color: var(--primary-color);
    box-shadow: 0 4px 16px rgba(var(--primary-rgb, 99, 102, 241), 0.1);
}

.formula-name {
    font-weight: 700;
    color: var(--text);
    margin-bottom: 12px;
    font-size: 16px;
}

.formula-expression {
    font-family: 'Courier New', monospace;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 16px;
    margin: 12px 0;
    font-size: 16px;
    color: var(--primary-color);
    font-weight: 600;
    overflow-x: auto;
}

.formula-description {
    font-size: 14px;
    color: var(--text-secondary);
    line-height: 1.6;
    margin-top: 12px;
}

.quiz-controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 32px;
    padding: 24px;
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 16px;
}

/* Light theme specific quiz control button styles */
:root:not(.dark) .quiz-controls button {
    background: var(--primary-color);
    border: 2px solid var(--primary-color);
    color: white;
    padding: 12px 24px;
    border-radius: 12px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

:root:not(.dark) .quiz-controls button:hover {
    background: rgba(99, 102, 241, 0.9);
    border-color: rgba(99, 102, 241, 0.9);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.3);
}

:root:not(.dark) .quiz-controls button:disabled {
    background: rgba(99, 102, 241, 0.3);
    border-color: rgba(99, 102, 241, 0.3);
    color: rgba(255, 255, 255, 0.7);
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.quiz-progress {
    flex: 1;
    margin: 0 20px;
}

.progress-bar {
    height: 8px;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 999px;
    overflow: hidden;
    margin-bottom: 8px;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-color), var(--primary-dark));
    transition: width 0.3s ease;
    border-radius: 999px;
}

.progress-text {
    font-size: 12px;
    color: var(--text-secondary);
    text-align: center;
    font-weight: 600;
}

.quiz-results {
    text-align: center;
    padding: 40px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.08);
    margin-top: 32px;
}

.results-icon {
    font-size: 4rem;
    margin-bottom: 16px;
}

.results-score {
    font-size: 2.5rem;
    font-weight: 900;
    margin-bottom: 8px;
}

.results-score.excellent {
    color: var(--success);
}

.results-score.good {
    color: var(--primary-color);
}

.results-score.average {
    color: var(--warning);
}

.results-score.poor {
    color: var(--danger);
}

.results-message {
    font-size: 16px;
    color: var(--text-secondary);
    margin-bottom: 24px;
}

.results-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 16px;
    margin-bottom: 24px;
}

.result-stat {
    padding: 12px;
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 12px;
}

.result-stat-value {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--text);
    display: block;
}

.result-stat-label {
    font-size: 12px;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.tab-instruction {
    text-align: center;
    color: var(--text-secondary);
    font-size: 16px;
    padding: 60px 20px;
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 16px;
    margin: 0;
}

.quiz-stat {
    text-align: center;
}

.quiz-stat-value {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary-color);
    display: block;
}

.quiz-stat-label {
    font-size: 12px;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    font-weight: 600;
}

.quiz-info {
    display: flex;
    justify-content: center;
    gap: 32px;
    margin-top: 16px;
    flex-wrap: wrap;
}

.quiz-header h2 {
    margin: 0 0 8px;
    font-size: 1.8rem;
    font-weight: 800;
    color: var(--text);
}

.question-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.question-number {
    background: var(--primary-color);
    color: white;
    padding: 8px 16px;
    border-radius: 999px;
    font-weight: 700;
    font-size: 14px;
}

.question-difficulty {
    padding: 4px 12px;
    border-radius: 999px;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
}

.question-difficulty.easy {
    background: var(--success-light);
    color: var(--success);
}

.question-difficulty.medium {
    background: var(--warning-light);
    color: var(--warning);
}

.question-difficulty.hard {
    background: var(--danger-light);
    color: var(--danger);
}

.question-text {
    font-size: 16px;
    font-weight: 600;
    color: var(--text);
    line-height: 1.6;
    margin-bottom: 20px;
}

.option-radio {
    width: 20px;
    height: 20px;
    border: 2px solid var(--border);
    border-radius: 50%;
    position: relative;
    flex-shrink: 0;
}

.option-item.selected .option-radio {
    border-color: var(--primary-color);
}

.option-item.selected .option-radio::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 10px;
    height: 10px;
    background: var(--primary-color);
    border-radius: 50%;
}

.option-item.correct {
    border-color: var(--success);
    background: var(--success-light);
    color: var(--success);
}

.option-item.incorrect {
    border-color: var(--danger);
    background: var(--danger-light);
    color: var(--danger);
}

.answer-explanation {
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 16px;
    margin-top: 16px;
    display: none;
}

.answer-explanation.show {
    display: block;
    animation: fadeInUp 0.3s ease-out;
}

.explanation-header {
    font-weight: 700;
    color: var(--text);
    margin-bottom: 8px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.explanation-text {
    font-size: 14px;
    color: var(--text-secondary);
    line-height: 1.6;
}

.result-indicator {
    padding: 4px 12px;
    border-radius: 999px;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
}

.result-indicator.correct {
    background: var(--success-light);
    color: var(--success);
}

.result-indicator.incorrect {
    background: var(--danger-light);
    color: var(--danger);
}

/* Problems Interface Styles */
.problems-container {
    max-width: 1000px;
    margin: 0 auto;
}

.problems-header {
    text-align: center;
    margin-bottom: 36px;
    padding: 32px;
    background: linear-gradient(135deg, var(--bg-elev) 0%, var(--bg-card) 100%);
    border-radius: 24px;
    border: 2px solid var(--border);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.08);
}

.problems-header h2 {
    margin: 0 0 8px;
    font-size: 1.8rem;
    font-weight: 800;
    color: var(--text);
}

.problems-info {
    display: flex;
    justify-content: center;
    gap: 32px;
    margin-top: 16px;
    flex-wrap: wrap;
}

.problems-stat {
    text-align: center;
}

.problems-stat-value {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary-color);
    display: block;
}

.problems-stat-label {
    font-size: 12px;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    font-weight: 600;
}

.problems-list {
    display: flex;
    flex-direction: column;
    gap: 24px;
}

.problem-card {
    background: var(--bg-card);
    border: 2px solid var(--border);
    border-radius: 20px;
    padding: 28px;
    box-shadow: 0 6px 24px rgba(0, 0, 0, 0.08);
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.problem-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(var(--primary-rgb, 99, 102, 241), 0.05), transparent);
    transition: left 0.6s;
}

.problem-card:hover::before {
    left: 100%;
}

.problem-card:hover {
    border-color: var(--primary-color);
    transform: translateY(-4px);
    box-shadow: 0 12px 40px rgba(var(--primary-rgb, 99, 102, 241), 0.15);
}

.problem-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.problem-number {
    background: var(--primary-color);
    color: white;
    padding: 8px 16px;
    border-radius: 999px;
    font-weight: 700;
    font-size: 14px;
}

.problem-difficulty {
    padding: 4px 12px;
    border-radius: 999px;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
}

.problem-difficulty.easy {
    background: var(--success-light);
    color: var(--success);
}

.problem-difficulty.medium {
    background: var(--warning-light);
    color: var(--warning);
}

.problem-difficulty.hard {
    background: var(--danger-light);
    color: var(--danger);
}

.problem-statement {
    font-size: 16px;
    font-weight: 600;
    color: var(--text);
    line-height: 1.7;
    margin-bottom: 24px;
    padding: 20px;
    background: var(--bg-elev);
    border: 1px solid var(--border);
    border-radius: 12px;
    border-left: 4px solid var(--primary-color);
}

.solution-toggle {
    margin-bottom: 20px;
}

.solution-btn {
    background: var(--bg-elev);
    border: 2px solid var(--border);
    color: var(--text);
    padding: 12px 20px;
    border-radius: 12px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
}

.solution-btn:hover {
    background: var(--primary-light);
    border-color: var(--primary-color);
    color: var(--primary-color);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(var(--primary-rgb, 99, 102, 241), 0.2);
}

.toggle-icon {
    font-size: 12px;
    transition: transform 0.3s ease;
}

.solution-content {
    background: var(--bg-elev);
    border: 2px solid var(--border);
    border-radius: 16px;
    padding: 24px;
    margin-top: 16px;
    animation: fadeInUp 0.4s ease-out;
}

.solution-section {
    margin-bottom: 20px;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--border);
}

.solution-section:last-child {
    margin-bottom: 0;
    padding-bottom: 0;
    border-bottom: none;
}

.solution-section h4 {
    font-size: 16px;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.solution-section h4::before {
    content: '▶';
    font-size: 12px;
    color: var(--primary-color);
}

.solution-section p {
    font-size: 15px;
    line-height: 1.7;
    color: yellow;
    margin: 0;
}

.solution-steps {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.solution-step {
    display: flex;
    align-items: flex-start;
    gap: 12px;
    padding: 16px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 12px;
    transition: all 0.3s ease;
}

.solution-step:hover {
    border-color: var(--primary-color);
    background: var(--primary-light);
    transform: translateX(4px);
}

.step-number {
    background: var(--primary-color);
    color: white;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 12px;
    font-weight: 700;
    flex-shrink: 0;
    margin-top: 2px;
}

.step-text {
    font-size: 15px;
    line-height: 1.6;
    color: var(--text);
    flex: 1;
}

.answer-section {
    background: linear-gradient(135deg, var(--success-light), rgba(34, 197, 94, 0.1));
    border: 2px solid var(--success);
    border-radius: 12px;
    padding: 20px;
}

.answer-section h4 {
    color: var(--success);
}

.final-answer {
    font-size: 18px;
    font-weight: 700;
    color: var(--success);
    background:var(--primary-color);
    padding: 16px;
    border-radius: 8px;
    border: 2px solid var(--success);
    text-align: center;
    font-family: 'Courier New', monospace;
}

.concept-section {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.1), rgba(139, 92, 246, 0.05));
    border: 2px solid var(--primary-color);
    border-radius: 12px;
    padding: 20px;
}

.concept-section h4 {
    color: var(--primary-color);
}

.concept-section p {
    color: var(--text);
    font-weight: 500;
}

/* Light theme specific problems styles */
:root:not(.dark) .solution-btn {
    background: rgba(99, 102, 241, 0.05);
    border: 2px solid rgba(99, 102, 241, 0.15);
    color: var(--primary-color);
}

:root:not(.dark) .solution-btn:hover {
    background: rgba(99, 102, 241, 0.1);
    border-color: rgba(99, 102, 241, 0.3);
    color: var(--primary-color);
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.2);
}

:root:not(.dark) .problem-statement {
    background: rgba(99, 102, 241, 0.05);
    border-color: rgba(99, 102, 241, 0.15);
    border-left-color: var(--primary-color);
}

:root:not(.dark) .solution-content {
    background: rgba(99, 102, 241, 0.03);
    border-color: rgba(99, 102, 241, 0.15);
}

:root:not(.dark) .solution-step {
    background: rgba(255, 255, 255, 0.8);
    border-color: rgba(99, 102, 241, 0.15);
}

:root:not(.dark) .solution-step:hover {
    background: rgba(99, 102, 241, 0.1);
    border-color: rgba(99, 102, 241, 0.3);
}

:root:not(.dark) .final-answer {
    background: rgba(34, 197, 94, 0.05);
    color: var(--success);
    border-color: var(--success);
}

/* Responsive design for problems */
@media (max-width: 768px) {
    .problems-header {
        padding: 24px;
    }
    
    .problems-info {
        gap: 20px;
    }
    
    .problem-card {
        padding: 20px;
    }
    
    .problem-header {
        flex-direction: column;
        gap: 12px;
        align-items: flex-start;
    }
    
    .solution-content {
        padding: 20px;
    }
    
    .solution-step {
        flex-direction: column;
        gap: 8px;
    }
    
    .step-number {
        align-self: flex-start;
    }
}

@media (max-width: 480px) {
    .problems-header h2 {
        font-size: 1.5rem;
    }
    
    .problems-info {
        flex-direction: column;
        gap: 16px;
    }
    
    .problem-card {
        padding: 16px;
    }
    
    .problem-statement {
        padding: 16px;
        font-size: 15px;
    }
    
    .solution-content {
        padding: 16px;
    }
    
    .final-answer {
        font-size: 16px;
        padding: 12px;
    }
}

/* ========================================
   DARK MODE STYLES
   ======================================== */

:root.dark {
    --study-bg: #0a0f1c;
    --study-bg-elev: #1a2332;
    --study-bg-card: #1e2936;
    --study-text: #f8fafc;
    --study-text-secondary: #cbd5e1;
    --study-muted: #94a3b8;
    --study-primary: #818cf8;
    --study-primary-dark: #6366f1;
    --study-success: #34d399;
    --study-danger: #f87171;
    --study-warning: #fbbf24;
    --study-border: #374151;
    --study-border-light: #4b5563;
    --study-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.5), 0 2px 4px -1px rgba(0, 0, 0, 0.4);
    --study-shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.6), 0 4px 6px -2px rgba(0, 0, 0, 0.5);
}

/* Main layout dark mode */
:root.dark .study-main {
    background: var(--study-bg);
    color: var(--study-text);
}

/* Subject selector dark mode */
:root.dark .subject-selector {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
}

:root.dark .subject-tab {
    background: var(--study-bg-card);
    color: var(--study-text-secondary);
    border: 1px solid var(--study-border);
}

:root.dark .subject-tab:hover {
    background: var(--study-primary);
    color: var(--study-bg);
    border-color: var(--study-primary);
}

:root.dark .subject-tab.active {
    background: var(--study-primary);
    color: var(--study-bg);
    border-color: var(--study-primary);
}

/* Study navigation dark mode */
:root.dark .study-nav {
    background: var(--study-bg-elev);
    border-right: 1px solid var(--study-border);
}

:root.dark .nav-header {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
}

:root.dark .progress-indicator {
    background: var(--study-bg-card);
    color: var(--study-text-secondary);
    border: 1px solid var(--study-border);
}

:root.dark .chapter-item {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .chapter-item:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

:root.dark .chapter-item.active {
    background: var(--study-primary);
    color: var(--study-bg);
    border-color: var(--study-primary);
}

:root.dark .chapter-item.active h3 {
    color: var(--study-bg);
}

:root.dark .status-badge {
    background: var(--study-bg-elev);
    color: var(--study-text-secondary);
}

:root.dark .status-badge.completed {
    background: var(--study-success);
    color: var(--study-bg);
}

/* Study content dark mode */
:root.dark .study-content {
    background: var(--study-bg);
    color: var(--study-text);
}

:root.dark .content-header {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
}

:root.dark .content-header h1 {
    color: var(--study-text);
}

:root.dark .tab-btn {
    background: var(--study-bg-card);
    color: var(--study-text-secondary);
    border: 1px solid var(--study-border);
}

:root.dark .tab-btn:hover {
    background: var(--study-bg-elev);
    color: var(--study-text);
}

:root.dark .tab-btn.active {
    background: var(--study-primary);
    color: var(--study-bg);
    border-color: var(--study-primary);
}

:root.dark .tab-panel {
    background: var(--study-bg);
    color: var(--study-text);
}

/* Welcome message dark mode */
:root.dark .welcome-message {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .feature-item {
    color: var(--study-text-secondary);
}

/* Chapter content dark mode */
:root.dark .chapter-content {
    background: var(--study-bg);
    color: var(--study-text);
}

:root.dark .chapter-header-actions {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
}

:root.dark .weightage-badge {
    background: var(--study-primary);
    color: var(--study-bg);
}

:root.dark .questions-count {
    background: var(--study-bg-card);
    color: var(--study-text-secondary);
    border: 1px solid var(--study-border);
}

:root.dark .chapter-intro {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
}

:root.dark .topics-grid {
    background: var(--study-bg);
}

:root.dark .topic-card {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .topic-card:hover {
    border-color: var(--study-primary);
    box-shadow: var(--study-shadow);
}

:root.dark .subtopics-section {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
}

:root.dark .subtopic-item {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .subtopic-item:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

:root.dark .subtopic-item h4 {
    color: var(--study-text);
}

/* Buttons dark mode */
:root.dark .btn.primary {
    background: var(--study-primary);
    color: var(--study-bg);
    border: 1px solid var(--study-primary);
}

:root.dark .btn.primary:hover {
    background: var(--study-primary-dark);
    border-color: var(--study-primary-dark);
}

:root.dark .btn.success {
    background: var(--study-success);
    color: var(--study-bg);
    border: 1px solid var(--study-success);
}

:root.dark .btn.success:hover {
    background: #10b981;
    border-color: #10b981;
}

:root.dark .btn.secondary {
    background: var(--study-bg-card);
    color: var(--study-text);
    border: 1px solid var(--study-border);
}

:root.dark .btn.secondary:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

:root.dark .completion-btn {
    background: var(--study-primary);
    color: var(--study-bg);
    border: 1px solid var(--study-primary);
}

:root.dark .completion-btn:hover {
    background: var(--study-primary-dark);
    border-color: var(--study-primary-dark);
}

/* Formulas dark mode */
:root.dark .formulas-content {
    background: var(--study-bg);
    color: var(--study-text);
}

:root.dark .formula-category {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
}

:root.dark .formula-item {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

/* Quiz dark mode */
:root.dark .quiz-content {
    background: var(--study-bg);
    color: var(--study-text);
}

:root.dark .quiz-container {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
}

:root.dark .quiz-header {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
}

:root.dark .question-card {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .option-item {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .option-item:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

:root.dark .option-item.selected {
    background: var(--study-primary);
    color: var(--study-bg);
    border-color: var(--study-primary);
}

:root.dark .quiz-controls button {
    background: var(--study-bg-card);
    color: var(--study-text);
    border: 1px solid var(--study-border);
}

:root.dark .quiz-controls button:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

:root.dark .quiz-controls button:disabled {
    background: var(--study-bg-elev);
    color: var(--study-muted);
    border-color: var(--study-border);
}

/* Problems dark mode */
:root.dark .problems-container {
    background: var(--study-bg);
    color: var(--study-text);
}

:root.dark .problems-header {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
}

:root.dark .problem-card {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .problem-statement {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .solution-content {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .solution-step {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .solution-step:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

:root.dark .final-answer {
    background: var(--study-success);
    color: var(--study-bg);
}

:root.dark .solution-btn {
    background: var(--study-bg-card);
    color: var(--study-text);
    border: 1px solid var(--study-border);
}

:root.dark .solution-btn:hover {
    background: var(--study-bg-elev);
    border-color: var(--study-primary);
}

/* Progress tracker dark mode */
:root.dark .progress-tracker {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
}

:root.dark .progress-item {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .progress-item.completed {
    background: var(--study-success);
    color: var(--study-bg);
    border-color: var(--study-success);
}

:root.dark .completion-indicator {
    background: var(--study-success);
    color: var(--study-bg);
}

/* Completion message dark mode */
:root.dark .completion-message {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
    box-shadow: var(--study-shadow-lg);
}

/* Tab instruction dark mode */
:root.dark .tab-instruction {
    color: var(--study-text-secondary);
}

/* Answer explanation dark mode */
:root.dark .answer-explanation {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .explanation-header {
    background: var(--study-bg-elev);
    border-bottom: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .explanation-text {
    color: var(--study-text-secondary);
}

/* Quiz results dark mode */
:root.dark .quiz-results {
    background: var(--study-bg-card);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

:root.dark .results-score {
    color: var(--study-text);
}

:root.dark .results-message {
    color: var(--study-text-secondary);
}

:root.dark .result-stat {
    background: var(--study-bg-elev);
    border: 1px solid var(--study-border);
    color: var(--study-text);
}

/* Quiz review dark mode */
:root.dark .quiz-review {
    background: var(--study-bg);
    color: var(--study-text);
}

:root.dark .result-indicator.correct {
    background: var(--study-success);
    color: var(--study-bg);
}

:root.dark .result-indicator.incorrect {
    background: var(--study-danger);
    color: var(--study-bg);
}

:root.dark .option-item.correct {
    background: var(--study-success);
    color: var(--study-bg);
    border-color: var(--study-success);
}

:root.dark .option-item.incorrect {
    background: var(--study-danger);
    color: var(--study-bg);
    border-color: var(--study-danger);
}