:root {
    /* Color Palette - Dark Mode with Vibrant Accents */
    --bg-primary: #0a0e27;
    --bg-secondary: #151b3d;
    --bg-tertiary: #1e2749;
    --bg-card: rgba(30, 39, 73, 0.6);
    --bg-card-hover: rgba(30, 39, 73, 0.9);
    
    --accent-primary: #6366f1;
    --accent-secondary: #8b5cf6;
    --accent-success: #10b981;
    --accent-warning: #f59e0b;
    --accent-gradient: linear-gradient(135deg, #6366f1 0%, #8b5cf6 100%);
    
    --text-primary: #f8fafc;
    --text-secondary: #cbd5e1;
    --text-tertiary: #94a3b8;
    
    --border-color: rgba(99, 102, 241, 0.2);
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 20px rgba(99, 102, 241, 0.3);
    
    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-heading: 'Poppins', sans-serif;
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    
    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

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

body {
    font-family: var(--font-primary);
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    overflow-x: hidden;
}

/* Animated Background */
body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: 
        radial-gradient(circle at 20% 50%, rgba(99, 102, 241, 0.1) 0%, transparent 50%),
        radial-gradient(circle at 80% 80%, rgba(139, 92, 246, 0.1) 0%, transparent 50%);
    pointer-events: none;
    z-index: 0;
}

/* Navigation */
.navbar {
    background: rgba(21, 27, 61, 0.8);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-md);
}

.nav-container {
    max-width: 1400px;
    margin: 0 auto;
    padding: var(--spacing-sm) var(--spacing-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    font-family: var(--font-heading);
    font-size: 1.5rem;
    font-weight: 700;
}

.logo-icon {
    font-size: 2rem;
    animation: float 3s ease-in-out infinite;
}

.logo-text .accent {
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

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

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: 8px;
    transition: all var(--transition-normal);
    font-weight: 500;
}

.nav-link:hover {
    color: var(--text-primary);
    background: rgba(99, 102, 241, 0.1);
}

.nav-link.active {
    color: var(--text-primary);
    background: var(--accent-gradient);
    box-shadow: var(--shadow-glow);
}

/* Main Content */
#app-content {
    position: relative;
    z-index: 1;
}

.page {
    display: none;
    animation: fadeIn 0.4s ease;
}

.page.active {
    display: block;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: var(--spacing-xl) var(--spacing-md);
}

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

.hero-title {
    font-family: var(--font-heading);
    font-size: 3rem;
    font-weight: 800;
    margin-bottom: var(--spacing-sm);
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
}

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-xl);
}

.stat-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-md);
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-sm);
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    background: var(--bg-card-hover);
}

.stat-icon {
    font-size: 2.5rem;
    animation: pulse 2s ease-in-out infinite;
}

.stat-value {
    font-family: var(--font-heading);
    font-size: 2rem;
    font-weight: 700;
    color: var(--accent-primary);
}

.stat-label {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* Modules Grid */
.modules-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
}

.module-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 20px;
    padding: var(--spacing-lg);
    text-align: center;
    transition: all var(--transition-normal);
    cursor: pointer;
    box-shadow: var(--shadow-sm);
}

.module-card:hover {
    transform: translateY(-8px) scale(1.02);
    box-shadow: var(--shadow-glow);
    border-color: var(--accent-primary);
}

.module-icon {
    font-size: 4rem;
    margin-bottom: var(--spacing-sm);
    animation: bounce 2s ease-in-out infinite;
}

.module-card h3 {
    font-family: var(--font-heading);
    font-size: 1.5rem;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

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

/* Buttons */
.btn {
    padding: var(--spacing-xs) var(--spacing-md);
    border: none;
    border-radius: 10px;
    font-family: var(--font-primary);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-normal);
    text-decoration: none;
    display: inline-block;
}

.btn-primary {
    background: var(--accent-gradient);
    color: var(--text-primary);
    box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

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

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

.btn-success {
    background: var(--accent-success);
    color: white;
}

.btn-success:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(16, 185, 129, 0.4);
}

/* Page Header */
.page-header {
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

.page-header h1 {
    font-family: var(--font-heading);
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
}

.page-header p {
    color: var(--text-secondary);
    font-size: 1.125rem;
}

/* Category Tabs */
.category-tabs {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
    flex-wrap: wrap;
    justify-content: center;
}

.tab-btn {
    padding: var(--spacing-xs) var(--spacing-md);
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    color: var(--text-secondary);
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

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

.tab-btn.active {
    background: var(--accent-gradient);
    color: var(--text-primary);
    border-color: transparent;
}

/* Flashcard */
.vocabulary-container {
    max-width: 700px;
    margin: 0 auto;
}

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

.control-btn {
    padding: var(--spacing-xs) var(--spacing-md);
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    color: var(--text-primary);
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-normal);
}

.control-btn:hover {
    background: var(--accent-gradient);
    box-shadow: var(--shadow-glow);
}

.card-counter {
    color: var(--text-secondary);
    font-weight: 600;
}

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

.flashcard {
    position: relative;
    width: 100%;
    height: 400px;
    transition: transform var(--transition-slow);
    transform-style: preserve-3d;
    cursor: pointer;
}

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

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 20px;
    padding: var(--spacing-xl);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 2px solid var(--border-color);
    box-shadow: var(--shadow-lg);
}

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

.word-display {
    font-family: var(--font-heading);
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent-primary);
    margin-bottom: var(--spacing-md);
}

.pronunciation-btn {
    margin-top: var(--spacing-md);
    padding: var(--spacing-sm) var(--spacing-lg);
    background: rgba(99, 102, 241, 0.2);
    border: 1px solid var(--accent-primary);
    border-radius: 12px;
    color: var(--text-primary);
    font-size: 1rem;
    cursor: pointer;
    transition: all var(--transition-normal);
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.pronunciation-btn:hover {
    background: var(--accent-gradient);
    transform: scale(1.05);
}

.definition {
    font-size: 1.5rem;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.example {
    font-size: 1.125rem;
    color: var(--text-secondary);
    font-style: italic;
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.phonetic {
    font-size: 1.25rem;
    color: var(--accent-secondary);
    font-family: monospace;
}

.mark-known {
    display: block;
    width: 100%;
    padding: var(--spacing-md);
    font-size: 1.125rem;
}

/* Pronunciation Page */
.pronunciation-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: var(--spacing-lg);
}

.pronunciation-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-sm);
}

.pronunciation-card h3 {
    font-family: var(--font-heading);
    font-size: 1.5rem;
    margin-bottom: var(--spacing-xs);
    color: var(--accent-primary);
}

.card-description {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

.pair-item,
.sound-item {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: var(--spacing-md);
    margin-bottom: var(--spacing-sm);
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: all var(--transition-normal);
}

.pair-item:hover,
.sound-item:hover {
    background: var(--bg-secondary);
    border-color: var(--accent-primary);
    transform: translateX(4px);
}

.pair-words {
    display: flex;
    gap: var(--spacing-md);
}

.pair-word,
.sound-word {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
}

.sound-btn {
    background: var(--accent-gradient);
    border: none;
    border-radius: 8px;
    padding: var(--spacing-xs) var(--spacing-sm);
    color: white;
    cursor: pointer;
    transition: all var(--transition-normal);
}

.sound-btn:hover {
    transform: scale(1.1);
    box-shadow: var(--shadow-glow);
}

/* Quiz */
.quiz-container {
    max-width: 800px;
    margin: 0 auto;
}

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

.quiz-type-btn {
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-lg);
    cursor: pointer;
    transition: all var(--transition-normal);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
}

.quiz-type-btn:hover {
    background: var(--bg-card-hover);
    border-color: var(--accent-primary);
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
}

.type-icon {
    font-size: 3rem;
}

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

.progress-bar {
    width: 100%;
    height: 12px;
    background: var(--bg-tertiary);
    border-radius: 10px;
    overflow: hidden;
    margin-bottom: var(--spacing-sm);
}

.progress-fill {
    height: 100%;
    background: var(--accent-gradient);
    transition: width var(--transition-normal);
    box-shadow: 0 0 10px rgba(99, 102, 241, 0.5);
}

.question-counter {
    color: var(--text-secondary);
    font-weight: 600;
}

.question-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-xl);
    margin-bottom: var(--spacing-md);
    box-shadow: var(--shadow-md);
}

.question-text {
    font-size: 1.75rem;
    margin-bottom: var(--spacing-lg);
    text-align: center;
    color: var(--text-primary);
}

.answers-grid {
    display: grid;
    gap: var(--spacing-sm);
}

.answer-btn {
    background: var(--bg-tertiary);
    border: 2px solid var(--border-color);
    border-radius: 12px;
    padding: var(--spacing-md);
    color: var(--text-primary);
    font-size: 1.125rem;
    cursor: pointer;
    transition: all var(--transition-normal);
    text-align: left;
}

.answer-btn:hover {
    background: var(--bg-secondary);
    border-color: var(--accent-primary);
    transform: translateX(4px);
}

.answer-btn.correct {
    background: rgba(16, 185, 129, 0.2);
    border-color: var(--accent-success);
}

.answer-btn.incorrect {
    background: rgba(239, 68, 68, 0.2);
    border-color: #ef4444;
}

.feedback {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-lg);
    text-align: center;
}

.feedback-content {
    margin-bottom: var(--spacing-md);
    font-size: 1.125rem;
}

.results-content {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 20px;
    padding: var(--spacing-xl);
    text-align: center;
    box-shadow: var(--shadow-lg);
}

.results-content h2 {
    font-family: var(--font-heading);
    font-size: 2.5rem;
    margin-bottom: var(--spacing-lg);
}

.score-display {
    margin: var(--spacing-xl) 0;
}

.score-circle {
    display: inline-flex;
    align-items: baseline;
    justify-content: center;
    width: 200px;
    height: 200px;
    border-radius: 50%;
    background: var(--accent-gradient);
    box-shadow: var(--shadow-glow);
    font-family: var(--font-heading);
}

.score-value {
    font-size: 4rem;
    font-weight: 700;
}

.score-total {
    font-size: 2rem;
    color: rgba(255, 255, 255, 0.8);
}

.score-message {
    font-size: 1.5rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
}

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

/* Progress Page */
.progress-grid {
    display: grid;
    gap: var(--spacing-lg);
}

.progress-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-sm);
}

.progress-card.full-width {
    grid-column: 1 / -1;
}

.progress-card h3 {
    font-family: var(--font-heading);
    font-size: 1.5rem;
    margin-bottom: var(--spacing-md);
    color: var(--accent-primary);
}

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

.stat-item {
    display: flex;
    justify-content: space-between;
    padding: var(--spacing-sm);
    background: var(--bg-tertiary);
    border-radius: 8px;
}

.stat-name {
    color: var(--text-secondary);
}

.stat-value-text {
    color: var(--accent-primary);
    font-weight: 700;
}

.achievements-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
    gap: var(--spacing-md);
}

.achievement {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: var(--spacing-md);
    background: var(--bg-tertiary);
    border: 2px solid var(--border-color);
    border-radius: 12px;
    text-align: center;
    transition: all var(--transition-normal);
}

.achievement.unlocked {
    border-color: var(--accent-success);
    background: rgba(16, 185, 129, 0.1);
}

.achievement.locked {
    opacity: 0.5;
}

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

.achievement-name {
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 4px;
}

.achievement-desc {
    font-size: 0.875rem;
    color: var(--text-tertiary);
}

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

.history-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md);
    background: var(--bg-tertiary);
    border-radius: 12px;
    border: 1px solid var(--border-color);
}

.empty-state {
    text-align: center;
    color: var(--text-tertiary);
    padding: var(--spacing-lg);
}

/* Utility Classes */
.hidden {
    display: none !important;
}

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

@keyframes float {
    0%, 100% {
        transform: translateY(0);
    }
    50% {
        transform: translateY(-10px);
    }
}

@keyframes pulse {
    0%, 100% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.1);
    }
}

@keyframes bounce {
    0%, 100% {
        transform: translateY(0);
    }
    50% {
        transform: translateY(-15px);
    }
}

/* Responsive Design */
@media (max-width: 768px) {
    .hero-title {
        font-size: 2rem;
    }
    
    .nav-menu {
        flex-wrap: wrap;
        justify-content: center;
    }
    
    .stats-grid {
        grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    }
    
    .modules-grid {
        grid-template-columns: 1fr;
    }
    
    .word-display {
        font-size: 2rem;
    }
    
    .pronunciation-grid {
        grid-template-columns: 1fr;
    }
    
    .results-actions {
        flex-direction: column;
    }
    
    .score-circle {
        width: 150px;
        height: 150px;
    }
    
    .score-value {
        font-size: 3rem;
    }
}