/* Cambridge Math Reviewer - Elegant & Classy Design */
/* Tailored Timeless Color Palette */

/* ===== CSS Variables ===== */
:root {
    /* Tailored Timeless Palette - Light Theme */
    --bg-primary: #F5F0E6;          /* White Sand tinted */
    --bg-secondary: #E6D7C3;        /* White Sand - main background */
    --bg-card: #FFFAF5;             /* Warm off-white */
    --bg-sidebar: #1E3A5F;          /* Dark Night - sidebar */

    --text-primary: #3D2E25;        /* Deep brown text */
    --text-secondary: #5D4037;      /* Carafe - secondary text */
    --text-muted: #8B7355;          /* Muted brown */
    --text-on-dark: #E6D7C3;        /* White Sand on dark */

    --border-color: #D4C4B0;        /* Muted border */
    --border-light: #EFE8DD;        /* Light border */

    /* Tailored Timeless Accent Colors */
    --accent-primary: #1E3A5F;      /* Dark Night - Navy Blue */
    --accent-secondary: #5D4037;    /* Carafe - Deep Brown */
    --accent-gold: #A08C3A;         /* Burnished Gold */
    --accent-mist: #A9C4D5;         /* Niagara Mist - Soft Blue */
    --accent-sand: #E6D7C3;         /* White Sand */

    /* Success/Error Colors - Palette-aligned */
    --success: #5D7A4A;             /* Muted green */
    --error: #A85A4A;               /* Muted red */
    --warning: #A08C3A;             /* Burnished Gold */

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;

    /* Border Radius - More subtle */
    --radius-sm: 3px;
    --radius-md: 6px;
    --radius-lg: 10px;
    --radius-pill: 50px;

    /* Shadows - Classic */
    --shadow-sm: 0 1px 3px rgba(44, 24, 16, 0.08);
    --shadow-md: 0 3px 10px rgba(44, 24, 16, 0.12);
    --shadow-lg: 0 8px 25px rgba(44, 24, 16, 0.15);
    --shadow-elegant: 0 2px 8px rgba(44, 24, 16, 0.1),
                      0 8px 32px rgba(44, 24, 16, 0.08);

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-normal: 300ms ease;
    --transition-slow: 500ms ease;
}

/* Dark Theme - Tailored Timeless */
body.dark-theme {
    --bg-primary: #0D1520;          /* Deep Dark Night */
    --bg-secondary: #142840;        /* Dark Navy */
    --bg-card: #1A314D;             /* Muted Navy */
    --bg-sidebar: #0A0F18;          /* Deepest Navy */

    --text-primary: #D4C5B0;        /* Lightened White Sand */
    --text-secondary: #A9C4D5;      /* Niagara Mist */
    --text-muted: #7A8A9A;          /* Muted Blue-Grey */
    --text-on-dark: #A9C4D5;        /* Niagara Mist */

    --border-color: #2A4058;        /* Navy border */
    --border-light: #1A314D;        /* Light Navy */

    --accent-primary: #6B9BD4;      /* Lightened Niagara Mist */
    --accent-secondary: #A08C3A;    /* Burnished Gold */
    --accent-gold: #C4A854;         /* Lightened Gold */
    --accent-mist: #9BB8CC;         /* Darker Niagara Mist */
    --accent-sand: #B8A892;         /* Darkened White Sand */

    --success: #7BA868;             /* Muted Green */
    --error: #C47A6A;               /* Muted Red */
    --warning: #C4A854;             /* Gold */

    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 3px 10px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 25px rgba(0, 0, 0, 0.5);
    --shadow-elegant: 0 2px 8px rgba(0, 0, 0, 0.35),
                      0 8px 32px rgba(0, 0, 0, 0.25);
}

/* ===== Reset & Base ===== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: 'Georgia', 'Times New Roman', serif;
    line-height: 1.7;
    color: var(--text-primary);
    background: var(--bg-primary);
    min-height: 100vh;
    overflow-x: hidden;
    transition: background-color var(--transition-normal), color var(--transition-normal);
}

/* Sans-serif for UI elements */
button, select, input, .stat-label, .stat-value,
.progress-label, .progress-value, .topic-tag,
.topic-level, .example-badge, .nav-item {
    font-family: 'Segoe UI', 'Garamond', serif;
}

/* ===== App Layout ===== */
.app-container {
    display: flex;
    min-height: 100vh;
}

/* ===== Sidebar ===== */
.sidebar {
    width: 280px;
    background: var(--bg-sidebar);
    padding: var(--spacing-lg);
    display: flex;
    flex-direction: column;
    position: fixed;
    height: 100vh;
    left: 0;
    top: 0;
    z-index: 100;
    transition: transform var(--transition-normal);
    border-right: 1px solid rgba(255, 255, 255, 0.1);
}

.sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--spacing-xl);
    padding-bottom: var(--spacing-md);
    border-bottom: 1px solid rgba(255, 255, 255, 0.15);
}

.sidebar-actions {
    display: flex;
    gap: var(--spacing-sm);
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-weight: 600;
    font-size: 1.1rem;
    color: var(--text-on-dark);
    letter-spacing: 0.5px;
}

.logo svg {
    color: var(--accent-gold);
}

.theme-toggle {
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: var(--radius-md);
    cursor: pointer;
    color: var(--text-on-dark);
    padding: var(--spacing-xs);
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background var(--transition-fast);
}

.theme-toggle:hover {
    background: rgba(255, 255, 255, 0.2);
}

.theme-toggle .moon-icon {
    display: none;
}

body.dark-theme .theme-toggle .sun-icon {
    display: none;
}

body.dark-theme .theme-toggle .moon-icon {
    display: block;
}

.sidebar-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    color: var(--text-on-dark);
    padding: var(--spacing-xs);
}

.nav {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.nav-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-sm) var(--spacing-md);
    border: none;
    background: transparent;
    border-radius: var(--radius-md);
    font-size: 0.95rem;
    font-weight: 500;
    color: rgba(245, 241, 232, 0.7);
    cursor: pointer;
    transition: all var(--transition-fast);
    text-align: left;
    letter-spacing: 0.3px;
}

.nav-item:hover {
    background: rgba(255, 255, 255, 0.08);
    color: var(--text-on-dark);
}

.nav-item.active {
    background: var(--accent-gold);
    color: #1A1E21;
}

.nav-item svg {
    flex-shrink: 0;
}

/* ===== Main Content ===== */
.main-content {
    flex: 1;
    margin-left: 280px;
    padding: var(--spacing-2xl);
    min-height: 100vh;
    background: var(--bg-primary);
    transition: background-color var(--transition-normal);
}

.page {
    display: none;
}

.page.active {
    display: block;
    animation: fadeIn 0.4s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.page-header {
    margin-bottom: var(--spacing-xl);
    padding-bottom: var(--spacing-md);
    border-bottom: 2px solid var(--border-light);
}

.page-header h1 {
    font-size: 2rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
    letter-spacing: -0.5px;
}

.subtitle {
    color: var(--text-muted);
    font-size: 1.05rem;
    font-style: italic;
}

/* ===== Cards ===== */
.card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-elegant);
    transition: box-shadow var(--transition-normal);
}

.card:hover {
    box-shadow: var(--shadow-lg);
}

/* ===== Stats Grid ===== */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-2xl);
}

.stat-card {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-lg);
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-normal);
    position: relative;
    overflow: hidden;
}

.stat-card::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 4px;
    background: var(--accent-primary);
}

.stat-card:nth-child(2)::before { background: var(--accent-mist); }
.stat-card:nth-child(3)::before { background: var(--accent-secondary); }
.stat-card:nth-child(4)::before { background: var(--accent-gold); }

.stat-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.stat-icon {
    width: 48px;
    height: 48px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-gold));
    color: white;
}

.stat-content {
    flex: 1;
}

.stat-value {
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--text-primary);
    font-family: 'Georgia', serif;
}

.stat-label {
    font-size: 0.85rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 1px;
}

/* ===== Categories Grid ===== */
.categories-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: var(--spacing-lg);
}

.category-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    cursor: pointer;
    transition: all var(--transition-normal);
    position: relative;
}

.category-card::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--accent-primary), var(--accent-gold));
    transform: scaleX(0);
    transition: transform var(--transition-normal);
}

.category-card:hover::after {
    transform: scaleX(1);
}

.category-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-lg);
}

.category-header {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.category-icon {
    width: 44px;
    height: 44px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-gold));
    color: white;
}

.category-name {
    font-size: 1.15rem;
    font-weight: 600;
    color: var(--text-primary);
    letter-spacing: 0.3px;
}

.category-description {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    font-style: italic;
}

.category-topics {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
}

.topic-tag {
    padding: 5px 12px;
    background: var(--bg-secondary);
    color: var(--accent-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-pill);
    font-size: 0.75rem;
    font-weight: 500;
    letter-spacing: 0.3px;
}

/* ===== Topics List ===== */
.topics-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.topic-section h2 {
    font-size: 1.4rem;
    font-weight: 600;
    color: var(--accent-primary);
    margin-bottom: var(--spacing-lg);
    padding-bottom: var(--spacing-sm);
    border-bottom: 2px solid var(--accent-gold);
    letter-spacing: 0.5px;
}

.topic-item {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    transition: all var(--transition-normal);
}

.topic-item:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--accent-gold);
}

.topic-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    cursor: pointer;
}

.topic-title {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.topic-level {
    padding: 5px 14px;
    border-radius: var(--radius-pill);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 1px;
}

.topic-level.foundation {
    background: var(--accent-mist);
    color: var(--accent-primary);
}

.topic-level.higher {
    background: var(--accent-secondary);
    color: white;
}

.topic-level.advanced {
    background: var(--accent-gold);
    color: white;
}

.topic-concepts {
    margin-top: var(--spacing-md);
    padding-top: var(--spacing-md);
    border-top: 1px solid var(--border-light);
    display: none;
}

.topic-concepts.show {
    display: block;
}

.concept-list {
    list-style: none;
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

.concept-item {
    padding: 6px 14px;
    background: var(--bg-secondary);
    border-radius: var(--radius-pill);
    font-size: 0.875rem;
    color: var(--text-secondary);
}

/* ===== Quiz Styles ===== */
.quiz-setup {
    max-width: 500px;
    margin: 0 auto;
}

.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-group label {
    display: block;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
    letter-spacing: 0.3px;
}

.form-group select,
.form-group input {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-family: inherit;
    background: var(--bg-card);
    color: var(--text-primary);
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.form-group select:focus,
.form-group input:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(30, 58, 95, 0.12);
}

.btn {
    padding: var(--spacing-sm) var(--spacing-lg);
    border: none;
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    letter-spacing: 0.3px;
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-gold));
    color: white;
    box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.btn-secondary:hover {
    background: var(--border-color);
}

.quiz-progress {
    margin-bottom: var(--spacing-lg);
}

.quiz-progress-bar {
    height: 6px;
    background: var(--bg-secondary);
    border-radius: var(--radius-pill);
    overflow: hidden;
    margin-bottom: var(--spacing-sm);
}

.quiz-progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-primary), var(--accent-gold));
    border-radius: var(--radius-pill);
    transition: width var(--transition-normal);
    width: 0%;
}

.quiz-question-card {
    max-width: 650px;
    margin: 0 auto;
}

.quiz-question-card h3 {
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-lg);
    line-height: 1.5;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.quiz-option {
    padding: var(--spacing-md) var(--spacing-lg);
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    text-align: left;
    font-size: 1rem;
    font-family: 'Georgia', serif;
    color: var(--text-primary);
}

.quiz-option:hover:not(.disabled) {
    border-color: var(--accent-primary);
    background: var(--bg-secondary);
}

.quiz-option.selected {
    border-color: var(--accent-primary);
    background: rgba(30, 58, 95, 0.08);
}

.quiz-option.correct {
    border-color: var(--success);
    background: rgba(93, 122, 74, 0.15);
}

.quiz-option.incorrect {
    border-color: var(--error);
    background: rgba(168, 90, 74, 0.12);
}

.quiz-option.disabled {
    cursor: default;
}

.quiz-feedback {
    margin-top: var(--spacing-lg);
    padding: var(--spacing-lg);
    border-radius: var(--radius-md);
    border-left: 4px solid;
    animation: fadeIn 0.3s ease;
}

.quiz-feedback.correct {
    background: rgba(93, 122, 74, 0.12);
    border-color: var(--success);
}

.quiz-feedback.incorrect {
    background: rgba(168, 90, 74, 0.1);
    border-color: var(--error);
}

.quiz-results {
    max-width: 500px;
    margin: 0 auto;
    text-align: center;
}

.results-card {
    text-align: center;
}

.score-circle {
    position: relative;
    width: 150px;
    height: 150px;
    margin: var(--spacing-xl) auto;
}

.score-circle svg {
    width: 100%;
    height: 100%;
}

.score-circle .score-text {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
}

/* ===== Flashcards ===== */
.flashcard-setup {
    max-width: 400px;
    margin: 0 auto;
}

.flashcard-active {
    max-width: 600px;
    margin: 0 auto;
    text-align: center;
}

.flashcard-counter {
    font-size: 0.95rem;
    color: var(--text-muted);
    margin-bottom: var(--spacing-md);
    font-style: italic;
}

.flashcard {
    perspective: 1000px;
    margin-bottom: var(--spacing-lg);
}

.flashcard-inner {
    position: relative;
    width: 100%;
    min-height: 280px;
    transition: transform 0.6s;
    transform-style: preserve-3d;
    cursor: pointer;
}

.flashcard.flipped .flashcard-inner {
    transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-xl);
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-elegant);
}

.flashcard-front p,
.flashcard-back p {
    font-size: 1.25rem;
    font-weight: 500;
    color: var(--text-primary);
    white-space: pre-wrap;
    line-height: 1.6;
}

.flashcard-hint {
    margin-top: var(--spacing-lg);
    font-size: 0.85rem;
    color: var(--text-muted);
    font-style: italic;
}

.flashcard-back {
    transform: rotateY(180deg);
    background: linear-gradient(135deg, rgba(160, 140, 58, 0.15), rgba(30, 58, 95, 0.15));
    border-color: var(--accent-gold);
}

.flashcard-controls {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
}

/* ===== Formulas ===== */
.formulas-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.formula-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    border-left: 4px solid var(--accent-primary);
}

.formula-card h3 {
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-lg);
}

.formula-list {
    display: grid;
    gap: var(--spacing-md);
}

.formula-item {
    padding: var(--spacing-md);
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
    border-left: 3px solid var(--accent-gold);
}

.formula-name {
    font-weight: 600;
    color: var(--accent-primary);
    margin-bottom: var(--spacing-xs);
}

.formula-expression {
    font-family: 'Times New Roman', serif;
    font-size: 1.2rem;
    font-style: italic;
    color: var(--text-primary);
    margin: var(--spacing-xs) 0;
}

.formula-notes {
    font-size: 0.875rem;
    color: var(--text-muted);
    font-style: italic;
}

/* ===== Progress ===== */
.progress-overview {
    margin-bottom: var(--spacing-xl);
}

.progress-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.progress-stat {
    text-align: center;
    padding: var(--spacing-lg);
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
}

.progress-label {
    display: block;
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: var(--spacing-xs);
    text-transform: uppercase;
    letter-spacing: 1px;
}

.progress-value {
    display: block;
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--accent-primary);
    font-family: 'Georgia', serif;
}

.progress-by-topic {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.topic-progress-item {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
}

.topic-progress-header {
    display: flex;
    justify-content: space-between;
    margin-bottom: var(--spacing-sm);
}

.topic-progress-name {
    font-weight: 500;
    color: var(--text-primary);
}

.topic-progress-score {
    font-weight: 600;
    color: var(--accent-primary);
}

.topic-progress-bar {
    height: 6px;
    background: var(--bg-secondary);
    border-radius: var(--radius-pill);
    overflow: hidden;
}

.topic-progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-primary), var(--accent-gold));
    border-radius: var(--radius-pill);
    transition: width var(--transition-normal);
}

/* ===== Topic Detail Page ===== */
.topic-detail-header {
    margin-bottom: var(--spacing-xl);
}

.back-btn {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-size: 0.9rem;
    cursor: pointer;
    transition: all var(--transition-fast);
    margin-bottom: var(--spacing-md);
    font-family: 'Segoe UI', sans-serif;
}

.back-btn:hover {
    background: var(--bg-secondary);
    border-color: var(--accent-primary);
}

.topic-breadcrumb {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-size: 0.95rem;
    color: var(--text-muted);
}

.topic-breadcrumb .category {
    color: var(--accent-primary);
    font-weight: 500;
}

.topic-detail-content {
    max-width: 900px;
}

.topic-overview-card {
    padding: var(--spacing-xl);
    margin-bottom: var(--spacing-lg);
    border-left: 4px solid var(--accent-gold);
}

.topic-overview-card h1 {
    font-size: 2rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
}

.topic-overview-card .topic-meta {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.topic-overview-card .description {
    font-size: 1.1rem;
    color: var(--text-secondary);
    line-height: 1.8;
}

.topic-tabs {
    display: flex;
    gap: var(--spacing-xs);
    margin-bottom: var(--spacing-lg);
    background: var(--bg-card);
    padding: var(--spacing-xs);
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-color);
    overflow-x: auto;
}

.topic-tab {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-lg);
    background: transparent;
    border: none;
    border-radius: var(--radius-md);
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
    white-space: nowrap;
    font-family: 'Segoe UI', sans-serif;
}

.topic-tab:hover {
    background: var(--bg-secondary);
    color: var(--text-primary);
}

.topic-tab.active {
    background: var(--accent-primary);
    color: white;
}

.tab-content {
    position: relative;
}

.tab-pane {
    display: none;
    animation: fadeIn 0.3s ease;
}

.tab-pane.active {
    display: block;
}

/* ===== Explanation Section ===== */
.explanation-section {
    margin-bottom: var(--spacing-xl);
}

.explanation-section h3 {
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-sm);
    border-bottom: 1px solid var(--border-light);
}

.concept-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
}

.concept-card h4 {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
}

.concept-card p {
    color: var(--text-secondary);
    line-height: 1.7;
}

.key-point {
    display: flex;
    align-items: flex-start;
    gap: var(--spacing-sm);
    padding: var(--spacing-md);
    background: rgba(93, 122, 74, 0.12);
    border-left: 3px solid var(--success);
    border-radius: var(--radius-md);
    margin-bottom: var(--spacing-sm);
}

.key-point::before {
    content: '✓';
    color: var(--success);
    font-weight: bold;
    flex-shrink: 0;
}

.warning-box {
    display: flex;
    align-items: flex-start;
    gap: var(--spacing-sm);
    padding: var(--spacing-md);
    background: rgba(160, 140, 58, 0.12);
    border-left: 3px solid var(--warning);
    border-radius: var(--radius-md);
    margin-bottom: var(--spacing-sm);
}

.warning-box::before {
    content: '!';
    color: var(--warning);
    font-weight: bold;
    flex-shrink: 0;
}

.info-box {
    display: flex;
    align-items: flex-start;
    gap: var(--spacing-sm);
    padding: var(--spacing-md);
    background: rgba(30, 58, 95, 0.08);
    border-left: 3px solid var(--accent-primary);
    border-radius: var(--radius-md);
    margin-bottom: var(--spacing-sm);
}

.info-box::before {
    content: 'i';
    color: var(--accent-primary);
    font-weight: bold;
    flex-shrink: 0;
}

/* ===== Examples Section ===== */
.example-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
}

.example-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--spacing-md);
}

.example-badge {
    padding: 5px 14px;
    background: var(--accent-primary);
    color: white;
    border-radius: var(--radius-pill);
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 1px;
}

.example-question {
    font-size: 1.1rem;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
}

.example-solution {
    background: rgba(93, 122, 74, 0.1);
    border-left: 3px solid var(--success);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
}

.solution-title {
    font-weight: 600;
    color: var(--success);
    margin-bottom: var(--spacing-sm);
}

.solution-steps {
    list-style: none;
    counter-reset: step-counter;
}

.solution-steps li {
    counter-increment: step-counter;
    margin-bottom: var(--spacing-sm);
    padding-left: var(--spacing-xl);
    position: relative;
    line-height: 1.6;
    color: var(--text-secondary);
}

.solution-steps li::before {
    content: counter(step-counter);
    position: absolute;
    left: 0;
    top: 0;
    width: 22px;
    height: 22px;
    background: var(--success);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    font-weight: 600;
}

.math-formula {
    font-family: 'Times New Roman', serif;
    font-size: 1.1rem;
    font-style: italic;
    background: var(--bg-secondary);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
}

/* ===== Practice Quiz Section ===== */
.topic-quiz-container {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
}

.topic-quiz-intro {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.topic-quiz-intro h3 {
    font-size: 1.5rem;
    margin-bottom: var(--spacing-sm);
}

.topic-question-card {
    margin-bottom: var(--spacing-lg);
}

.topic-question-text {
    font-size: 1.15rem;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
}

.topic-question-options {
    display: grid;
    gap: var(--spacing-sm);
}

.topic-question-option {
    padding: var(--spacing-md);
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    text-align: left;
    font-size: 1rem;
    font-family: 'Georgia', serif;
    color: var(--text-primary);
}

.topic-question-option:hover:not(.disabled) {
    border-color: var(--accent-primary);
    background: var(--bg-secondary);
}

.topic-question-option.correct {
    border-color: var(--success);
    background: rgba(93, 122, 74, 0.15);
}

.topic-question-option.incorrect {
    border-color: var(--error);
    background: rgba(168, 90, 74, 0.12);
}

.topic-question-option.disabled {
    cursor: default;
}

.topic-feedback {
    margin-top: var(--spacing-md);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    border-left: 4px solid;
    display: none;
}

.topic-feedback.show {
    display: block;
}

.topic-feedback.correct {
    background: rgba(93, 122, 74, 0.12);
    border-color: var(--success);
}

.topic-feedback.incorrect {
    background: rgba(168, 90, 74, 0.1);
    border-color: var(--error);
}

/* ===== Formulas Section ===== */
.formula-section {
    margin-bottom: var(--spacing-xl);
}

.formula-section h3 {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
}

.formula-display {
    background: linear-gradient(135deg, rgba(30, 58, 95, 0.06), rgba(160, 140, 58, 0.06));
    padding: var(--spacing-lg);
    border-radius: var(--radius-md);
    text-align: center;
    margin: var(--spacing-md) 0;
    border: 1px solid var(--border-color);
}

.formula-display .formula {
    font-family: 'Times New Roman', serif;
    font-size: 1.5rem;
    font-style: italic;
    color: var(--text-primary);
}

.formula-display .formula-name {
    font-size: 0.9rem;
    color: var(--text-muted);
    margin-top: var(--spacing-sm);
}

.formula-notes {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.mnemonic-card {
    background: linear-gradient(135deg, rgba(160, 140, 58, 0.12), rgba(93, 64, 55, 0.08));
    border: 1px solid var(--accent-gold);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
}

.mnemonic-title {
    font-weight: 600;
    color: var(--accent-gold);
    margin-bottom: var(--spacing-sm);
}

.mnemonic-content {
    font-family: 'Courier New', monospace;
    font-size: 1rem;
    color: var(--text-primary);
    background: var(--bg-card);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    white-space: pre-line;
}

.mnemonic-example {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-top: var(--spacing-sm);
    font-style: italic;
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .sidebar-toggle {
        display: block;
    }

    .main-content {
        margin-left: 0;
        padding: var(--spacing-lg);
    }

    .page-header h1 {
        font-size: 1.5rem;
    }

    .stats-grid {
        grid-template-columns: 1fr;
    }

    .categories-grid {
        grid-template-columns: 1fr;
    }

    .topic-tabs {
        flex-wrap: nowrap;
        -webkit-overflow-scrolling: touch;
    }

    .topic-overview-card h1 {
        font-size: 1.5rem;
    }

    .formula-display .formula {
        font-size: 1.2rem;
    }
}