/* ===== CSS Reset & Base Styles ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    /* Dark Grey Color Palette */
    --bg-primary: #1a1a1a;
    --bg-secondary: #252525;
    --bg-tertiary: #2d2d2d;
    --bg-hover: #353535;
    
    --text-primary: #e0e0e0;
    --text-secondary: #b0b0b0;
    --text-muted: #808080;
    
    --accent-primary: #4a9eff;
    --accent-hover: #3d8ae6;
    --accent-dark: #2a6bb8;
    
    --border-color: #404040;
    --shadow: rgba(0, 0, 0, 0.3);
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    
    /* Transitions */
    --transition: all 0.3s ease;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
}

/* ===== Global Link Styles ===== */
a {
    color: #8ec5fc;
    text-decoration: none;
    transition: var(--transition);
}

a:hover {
    color: #b3d9ff;
    text-decoration: underline;
}

a:visited {
    color: #a8c9f0;
}

/* Content area links */
.lesson-content a,
.content-section a:not(.btn-primary):not(.btn-secondary),
table a {
    color: #8ec5fc;
    text-decoration: underline;
    text-decoration-color: rgba(142, 197, 252, 0.3);
    text-underline-offset: 2px;
}

.lesson-content a:hover,
.content-section a:not(.btn-primary):not(.btn-secondary):hover,
table a:hover {
    color: #b3d9ff;
    text-decoration-color: rgba(179, 217, 255, 0.6);
}

/* ===== Top Navigation Bar ===== */
.top-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 70px;
    background-color: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 var(--spacing-lg);
    z-index: 1000;
    box-shadow: 0 2px 10px var(--shadow);
}

.nav-brand h1 {
    font-size: 1.5rem;
    background: linear-gradient(135deg, var(--accent-primary), #6bb6ff);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--spacing-md);
}

.nav-menu a {
    color: var(--text-secondary);
    text-decoration: none;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: 6px;
    transition: var(--transition);
    font-weight: 500;
}

.nav-menu a:hover,
.nav-menu a.active {
    color: var(--text-primary);
    background-color: var(--bg-hover);
}

.nav-user {
    display: flex;
    gap: var(--spacing-sm);
}

/* ===== Buttons ===== */
.btn-primary {
    background-color: var(--accent-primary);
    color: white;
    border: none;
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: 6px;
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

.btn-primary:hover {
    background-color: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(74, 158, 255, 0.3);
}

.btn-secondary {
    background-color: transparent;
    color: var(--text-primary);
    border: 2px solid var(--border-color);
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: 6px;
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

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

.btn-large {
    padding: var(--spacing-sm) var(--spacing-lg);
    font-size: 1.1rem;
}

/* ===== Container Layout ===== */
.container {
    display: flex;
    margin-top: 70px; /* Height of top nav */
    min-height: calc(100vh - 70px);
}

/* ===== Side Navigation Bar ===== */
.side-nav {
    position: fixed;
    left: 0;
    width: 260px;
    height: calc(100vh - 70px);
    background-color: var(--bg-secondary);
    border-right: 1px solid var(--border-color);
    padding: var(--spacing-lg);
    overflow-y: auto;
}

.side-nav h3 {
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
    font-size: 1.2rem;
}

.side-menu,
.quick-links {
    list-style: none;
}

.side-menu li,
.quick-links li {
    margin-bottom: var(--spacing-xs);
}

.side-menu a,
.quick-links a {
    display: block;
    color: var(--text-secondary);
    text-decoration: none;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: 6px;
    transition: var(--transition);
}

.side-menu a:hover,
.quick-links a:hover {
    color: var(--text-primary);
    background-color: var(--bg-hover);
    transform: translateX(4px);
}

/* Dropdown Menu in Side Nav */
.side-menu .dropdown {
    position: relative;
}

.side-menu .dropdown-toggle {
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
}

.side-menu .dropdown-toggle .arrow {
    font-size: 0.8rem;
    transition: var(--transition);
    padding: var(--spacing-xs);
    margin: calc(-1 * var(--spacing-xs));
    border-radius: 4px;
    cursor: pointer;
}

.side-menu .dropdown-toggle .arrow:hover {
    background-color: var(--bg-hover);
}

.side-menu .dropdown.open .dropdown-toggle .arrow {
    transform: rotate(90deg);
}

.side-menu .dropdown-menu {
    list-style: none;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.3s ease;
    padding-left: var(--spacing-sm);
    margin-top: var(--spacing-xs);
}

.side-menu .dropdown.open .dropdown-menu {
    max-height: 200px;
}

.side-menu .dropdown-menu li {
    margin-bottom: 0;
}

.side-menu .dropdown-menu a {
    padding: var(--spacing-xs) var(--spacing-sm);
    font-size: 0.95rem;
    border-left: 2px solid var(--border-color);
    border-radius: 0 6px 6px 0;
    margin-left: var(--spacing-xs);
}

.side-menu .dropdown-menu a:hover {
    border-left-color: var(--accent-primary);
    transform: translateX(4px);
}

.side-nav-footer {
    margin-top: var(--spacing-xl);
    padding-top: var(--spacing-lg);
    border-top: 1px solid var(--border-color);
}

.side-nav-footer h4 {
    color: var(--text-secondary);
    font-size: 0.9rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: var(--spacing-sm);
}

/* Custom Scrollbar for Side Nav */
.side-nav::-webkit-scrollbar {
    width: 8px;
}

.side-nav::-webkit-scrollbar-track {
    background: var(--bg-secondary);
}

.side-nav::-webkit-scrollbar-thumb {
    background: var(--bg-hover);
    border-radius: 4px;
}

.side-nav::-webkit-scrollbar-thumb:hover {
    background: var(--border-color);
}

/* ===== Main Content Area ===== */
.main-content {
    margin-left: 260px; /* Width of side nav */
    flex: 1;
    padding: var(--spacing-xl);
    max-width: 1200px;
}

/* ===== Hero Section ===== */
.hero {
    text-align: center;
    padding: var(--spacing-xl) 0;
    margin-bottom: var(--spacing-xl);
}

.hero h1 {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
    background: linear-gradient(135deg, var(--text-primary), var(--accent-primary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero p {
    font-size: 1.3rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
}

.cta-buttons {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    margin-top: var(--spacing-lg);
}

/* ===== Content Sections ===== */
.content-section {
    margin-bottom: var(--spacing-xl);
}

.content-section h2 {
    font-size: 2rem;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
}

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

.card-link-wrapper {
    text-decoration: none;
    color: inherit;
    display: block;
}

.card-link-wrapper:hover {
    text-decoration: none;
}

.card {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: var(--spacing-lg);
    transition: var(--transition);
    cursor: pointer;
    height: 100%;
}

.card:hover {
    transform: translateY(-8px);
    box-shadow: 0 8px 24px var(--shadow);
    border-color: var(--accent-primary);
}

.card-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.card h3 {
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
    font-size: 1.4rem;
}

.card p {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    line-height: 1.6;
}

.card-link {
    color: var(--accent-primary);
    text-decoration: none;
    font-weight: 600;
    display: inline-flex;
    align-items: center;
    transition: var(--transition);
}

.card-link-wrapper:hover .card-link {
    color: var(--accent-hover);
    transform: translateX(4px);
}

/* ===== Progress Bars ===== */
.progress-container {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: var(--spacing-lg);
}

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

.progress-item:last-child {
    margin-bottom: 0;
}

.progress-label {
    display: block;
    color: var(--text-primary);
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.progress-bar {
    width: 100%;
    height: 12px;
    background-color: var(--bg-tertiary);
    border-radius: 6px;
    overflow: hidden;
    margin-bottom: var(--spacing-xs);
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-primary), #6bb6ff);
    border-radius: 6px;
    transition: width 0.5s ease;
}

.progress-text {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

/* ===== Responsive Design ===== */
@media (max-width: 768px) {
    .side-nav {
        display: none; /* Hide side nav on mobile, can be toggled with JS */
    }
    
    .main-content {
        margin-left: 0;
        padding: var(--spacing-md);
    }
    
    .top-nav {
        padding: 0 var(--spacing-md);
    }
    
    .nav-menu {
        display: none; /* Can be shown in mobile menu */
    }
    
    .hero h1 {
        font-size: 2rem;
    }
    
    .hero p {
        font-size: 1.1rem;
    }
    
    .cta-buttons {
        flex-direction: column;
    }
    
    .card-grid {
        grid-template-columns: 1fr;
    }
}

/* ===== Additional Lesson Page Styles ===== */

/* Breadcrumb Navigation */
.breadcrumb {
    padding: var(--spacing-sm) 0;
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.breadcrumb a {
    color: var(--accent-primary);
    text-decoration: none;
}

.breadcrumb a:hover {
    text-decoration: underline;
}

/* Lesson Header */
.lesson-header {
    margin-bottom: var(--spacing-xl);
}

.lesson-header h1 {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-sm);
}

.lesson-header p {
    color: var(--text-secondary);
    font-size: 1.2rem;
}

.lesson-hero {
    padding: var(--spacing-lg) 0;
}

.lesson-icon {
    font-size: 4rem;
    margin-bottom: var(--spacing-md);
}

/* Data Tables */
.data-table {
    width: 100%;
    border-collapse: collapse;
    background-color: var(--bg-secondary);
    border-radius: 12px;
    overflow: hidden;
    margin: var(--spacing-md) 0;
}

.data-table thead {
    background-color: var(--bg-tertiary);
}

.data-table th,
.data-table td {
    padding: var(--spacing-sm) var(--spacing-md);
    text-align: left;
    border-bottom: 1px solid var(--border-color);
    border-right: 1px solid var(--border-color);
}

.data-table th:last-child,
.data-table td:last-child {
    border-right: none;
}

.data-table th {
    font-weight: 600;
    color: var(--text-primary);
}

.data-table td {
    color: var(--text-secondary);
}

.data-table tbody tr:hover {
    background-color: var(--bg-hover);
}

.data-table .letter {
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--accent-primary);
}

/* Highlight Classes */
.highlight-blue {
    background-color: #a8d4f0;
    color: #000000 !important;
}

/* Info Box */
.info-box {
    background-color: var(--bg-secondary);
    border-left: 4px solid var(--accent-primary);
    border-radius: 0 12px 12px 0;
    padding: var(--spacing-md);
    margin: var(--spacing-md) 0;
}

.info-box h4 {
    color: var(--accent-primary);
    margin-bottom: var(--spacing-sm);
}

.info-box ul {
    margin-left: var(--spacing-md);
}

.info-box li {
    margin-bottom: var(--spacing-xs);
    color: var(--text-secondary);
}

/* Lesson Content */
.lesson-content {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
}

.lesson-content p {
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
}

/* Lesson Navigation */
.lesson-nav {
    display: flex;
    justify-content: space-between;
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
}

/* Tone Cards */
.tone-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
}

.tone-card {
    background-color: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: var(--spacing-md);
    text-align: center;
    transition: var(--transition);
}

.tone-card:hover {
    border-color: var(--accent-primary);
    transform: translateY(-4px);
}

.tone-example {
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent-primary);
    margin-bottom: var(--spacing-xs);
}

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

.tone-description {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-xs);
}

.tone-meaning {
    font-style: italic;
    color: var(--text-muted);
}

/* Syllable Diagram */
.syllable-diagram {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-lg);
    background-color: var(--bg-tertiary);
    border-radius: 12px;
    margin: var(--spacing-md) 0;
}

.syllable-part {
    background-color: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: 8px;
    padding: var(--spacing-md);
    text-align: center;
}

.syllable-part .part-name {
    display: block;
    font-weight: 600;
    color: var(--text-primary);
}

.syllable-part .part-optional {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.syllable-part .part-required {
    font-size: 0.8rem;
    color: var(--accent-primary);
}

.syllable-diagram .plus {
    font-size: 1.5rem;
    color: var(--text-muted);
}

/* Example Box */
.example-box {
    background-color: var(--bg-tertiary);
    border-radius: 12px;
    padding: var(--spacing-lg);
    margin: var(--spacing-md) 0;
}

/* Grammar Note */
grammar-note,
.grammar-note {
    display: block;
    color: var(--text-muted);
    font-size: 0.9rem;
    font-style: italic;
    margin-top: var(--spacing-sm);
}

.example {
    text-align: center;
}

.example .vietnamese {
    display: block;
    font-size: 2rem;
    font-weight: 600;
    color: var(--accent-primary);
    margin-bottom: var(--spacing-md);
}

.example .breakdown {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.example .part {
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: 6px;
    font-weight: 500;
}

.example .subject {
    background-color: #2d5a4a;
    color: #8cd4b5;
}

.example .verb {
    background-color: #5a3d2d;
    color: #d4a88c;
}

.example .object {
    background-color: #3d2d5a;
    color: #a88cd4;
}

.example .translation {
    display: block;
    color: var(--text-secondary);
    font-style: italic;
}

/* Nav Brand Link */
.nav-brand a {
    text-decoration: none;
}

.nav-brand a h1 {
    font-size: 1.5rem;
    background: linear-gradient(135deg, var(--accent-primary), #6bb6ff);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}