/* CSS Variables */
:root {
    /* Colors */
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --secondary-color: #6366f1;
    --accent-color: #10b981;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    
    /* Grays */
    --gray-50: #f9fafb;
    --gray-100: #f3f4f6;
    --gray-200: #e5e7eb;
    --gray-300: #d1d5db;
    --gray-400: #9ca3af;
    --gray-500: #6b7280;
    --gray-600: #4b5563;
    --gray-700: #374151;
    --gray-800: #1f2937;
    --gray-900: #111827;
    
    /* Semantic colors */
    --text-primary: var(--gray-900);
    --text-secondary: var(--gray-600);
    --text-muted: var(--gray-500);
    --bg-primary: #ffffff;
    --bg-secondary: var(--gray-50);
    --bg-tertiary: var(--gray-100);
    --border-color: var(--gray-200);
    
    /* Typography */
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', sans-serif;
    --font-mono: 'Fira Code', 'SF Mono', 'Monaco', 'Cascadia Code', monospace;
    
    /* Spacing */
    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-5: 1.25rem;
    --space-6: 1.5rem;
    --space-8: 2rem;
    --space-10: 2.5rem;
    --space-12: 3rem;
    --space-16: 4rem;
    --space-20: 5rem;
    --space-24: 6rem;
    
    /* Sizing */
    --container-max-width: 1200px;
    --border-radius-sm: 0.375rem;
    --border-radius-md: 0.5rem;
    --border-radius-lg: 0.75rem;
    --border-radius-xl: 1rem;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    /* Transitions */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-normal: 300ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 500ms cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
    scroll-behavior: smooth;
}

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

/* Container */
.container {
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--space-6);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    line-height: 1.2;
    font-weight: 600;
}

.highlight {
    background: linear-gradient(120deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-3) var(--space-6);
    border: none;
    border-radius: var(--border-radius-lg);
    font-family: inherit;
    font-weight: 500;
    text-decoration: none;
    cursor: pointer;
    transition: all var(--transition-normal);
    transform: translateY(0);
}

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

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

.btn-secondary {
    background: var(--bg-primary);
    color: var(--text-primary);
    border: 2px solid var(--border-color);
}

.btn-secondary:hover {
    border-color: var(--primary-color);
    color: var(--primary-color);
    transform: translateY(-2px);
}

.btn-icon {
    font-size: 1.1em;
}

/* Header */
.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
}

.header-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 70px;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    font-weight: 700;
    font-size: 1.25rem;
    color: var(--text-primary);
}

.logo-icon {
    font-size: 1.5rem;
}

.nav {
    display: flex;
    align-items: center;
    gap: var(--space-8);
}

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    transition: color var(--transition-normal);
    position: relative;
}

.nav-link:hover {
    color: var(--primary-color);
}

.nav-link.cta {
    background: var(--primary-color);
    color: white;
    padding: var(--space-2) var(--space-4);
    border-radius: var(--border-radius-md);
}

.nav-link.cta:hover {
    background: var(--primary-hover);
    color: white;
}

.nav-toggle {
    display: none;
    flex-direction: column;
    gap: 4px;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--space-2);
}

.nav-toggle span {
    width: 25px;
    height: 3px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: all var(--transition-normal);
}

/* Hero Section */
.hero {
    position: relative;
    min-height: 100vh;
    display: flex;
    align-items: center;
    background: linear-gradient(135deg, var(--bg-primary) 0%, var(--bg-secondary) 100%);
    overflow: hidden;
}

.hero-background {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    opacity: 0.05;
}

.hero-grid {
    width: 100%;
    height: 100%;
    background-image: 
        linear-gradient(var(--primary-color) 1px, transparent 1px),
        linear-gradient(90deg, var(--primary-color) 1px, transparent 1px);
    background-size: 50px 50px;
    animation: grid-move 20s linear infinite;
}

@keyframes grid-move {
    0% { transform: translate(0, 0); }
    100% { transform: translate(50px, 50px); }
}

.hero-content {
    position: relative;
    z-index: 2;
    text-align: center;
    max-width: 800px;
    margin: 0 auto;
    padding: var(--space-24) 0;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: var(--space-2);
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-xl);
    padding: var(--space-2) var(--space-4);
    margin-bottom: var(--space-6);
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-secondary);
    box-shadow: var(--shadow-sm);
}

.badge-icon {
    font-size: 1rem;
}

.hero-title {
    font-size: clamp(2.5rem, 5vw, 4rem);
    font-weight: 700;
    margin-bottom: var(--space-6);
    line-height: 1.1;
}

.hero-description {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-8);
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: var(--space-12);
    margin-bottom: var(--space-10);
}

.stat {
    text-align: center;
}

.stat-number {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--primary-color);
    line-height: 1;
    margin-bottom: var(--space-1);
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
}

.hero-actions {
    display: flex;
    justify-content: center;
    gap: var(--space-4);
    flex-wrap: wrap;
}

/* Section Styling */
section {
    padding: var(--space-24) 0;
}

.section-header {
    text-align: center;
    margin-bottom: var(--space-16);
}

.section-title {
    font-size: clamp(2rem, 4vw, 3rem);
    font-weight: 700;
    margin-bottom: var(--space-4);
}

.section-description {
    font-size: 1.125rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
}

/* Overview Section */
.overview {
    background: var(--bg-secondary);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--space-8);
}

.feature-card {
    background: var(--bg-primary);
    padding: var(--space-8);
    border-radius: var(--border-radius-xl);
    box-shadow: var(--shadow-sm);
    text-align: center;
    transition: all var(--transition-normal);
    border: 1px solid var(--border-color);
}

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

.feature-icon {
    font-size: 3rem;
    margin-bottom: var(--space-4);
}

.feature-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--space-3);
}

.feature-description {
    color: var(--text-secondary);
    line-height: 1.6;
}

/* Curriculum Section */
.curriculum-timeline {
    display: flex;
    flex-direction: column;
    gap: var(--space-6);
}

.chapter-card {
    display: flex;
    gap: var(--space-6);
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-xl);
    padding: var(--space-8);
    transition: all var(--transition-normal);
    position: relative;
    overflow: hidden;
}

.chapter-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
}

.chapter-card:hover {
    transform: translateX(8px);
    box-shadow: var(--shadow-lg);
}

.chapter-number {
    flex-shrink: 0;
    width: 60px;
    height: 60px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    font-weight: 700;
    box-shadow: var(--shadow-md);
}

.chapter-content {
    flex: 1;
}

.chapter-title {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: var(--space-2);
}

.chapter-duration {
    display: inline-block;
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    padding: var(--space-1) var(--space-3);
    border-radius: var(--border-radius-md);
    font-size: 0.875rem;
    font-weight: 500;
    margin-bottom: var(--space-3);
}

.chapter-description {
    color: var(--text-secondary);
    margin-bottom: var(--space-4);
    line-height: 1.6;
}

.chapter-topics {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-2);
    margin-bottom: var(--space-4);
}

.topic-tag {
    background: var(--primary-color);
    color: white;
    padding: var(--space-1) var(--space-3);
    border-radius: var(--border-radius-md);
    font-size: 0.75rem;
    font-weight: 500;
}

.chapter-link {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 500;
    transition: color var(--transition-normal);
}

.chapter-link:hover {
    color: var(--primary-hover);
}

/* Demos Section */
.demos {
    background: var(--bg-secondary);
}

.demo-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: var(--space-8);
}

.demo-card {
    background: var(--bg-primary);
    border-radius: var(--border-radius-xl);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
    transition: all var(--transition-normal);
    border: 1px solid var(--border-color);
}

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

.demo-preview {
    padding: var(--space-6);
    background: var(--bg-tertiary);
}

.demo-browser {
    background: white;
    border-radius: var(--border-radius-md);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
}

.browser-header {
    background: var(--gray-100);
    padding: var(--space-3);
    border-bottom: 1px solid var(--border-color);
}

.browser-dots {
    display: flex;
    gap: var(--space-2);
}

.browser-dots span {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: var(--gray-400);
}

.browser-dots span:nth-child(1) { background: #ff5f57; }
.browser-dots span:nth-child(2) { background: #ffbd2e; }
.browser-dots span:nth-child(3) { background: #28ca42; }

.browser-content {
    padding: var(--space-4);
    min-height: 120px;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* Demo Content Styles */
.demo-basic {
    text-align: center;
}

.demo-basic h3 {
    color: var(--primary-color);
    margin-bottom: var(--space-2);
}

.demo-basic p {
    color: var(--text-secondary);
    margin-bottom: var(--space-3);
}

.demo-btn {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: var(--space-2) var(--space-4);
    border-radius: var(--border-radius-md);
    cursor: pointer;
}

.demo-responsive {
    width: 100%;
}

.demo-card-responsive {
    background: white;
    border-radius: var(--border-radius-md);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
}

.card-image {
    height: 60px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
}

.card-content {
    padding: var(--space-3);
}

.card-content h4 {
    font-size: 0.875rem;
    margin-bottom: var(--space-1);
}

.card-content p {
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.demo-grid-layout {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-2);
    width: 100%;
}

.grid-item {
    background: var(--primary-color);
    color: white;
    padding: var(--space-3);
    border-radius: var(--border-radius-md);
    text-align: center;
    font-weight: 600;
}

.demo-animation {
    width: 100%;
    text-align: center;
}

.animated-box {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 60px;
    height: 60px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-radius: 50%;
    font-size: 1.5rem;
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 20%, 50%, 80%, 100% { transform: translateY(0); }
    40% { transform: translateY(-10px); }
    60% { transform: translateY(-5px); }
}

.demo-info {
    padding: var(--space-6);
}

.demo-title {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--space-2);
}

.demo-description {
    color: var(--text-secondary);
    margin-bottom: var(--space-4);
    line-height: 1.6;
}

.demo-link {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 500;
    transition: color var(--transition-normal);
}

.demo-link:hover {
    color: var(--primary-hover);
}

/* Start Section */
.start {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
}

.start-content {
    text-align: center;
    max-width: 800px;
    margin: 0 auto;
}

.start-title {
    font-size: clamp(2rem, 4vw, 3rem);
    font-weight: 700;
    margin-bottom: var(--space-6);
}

.start-description {
    font-size: 1.125rem;
    margin-bottom: var(--space-12);
    opacity: 0.9;
}

.start-options {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--space-6);
}

.option-card {
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: var(--border-radius-xl);
    padding: var(--space-8);
    text-align: center;
    transition: all var(--transition-normal);
}

.option-card:hover {
    transform: translateY(-4px);
    background: rgba(255, 255, 255, 0.15);
}

.option-icon {
    font-size: 3rem;
    margin-bottom: var(--space-4);
}

.option-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--space-3);
}

.option-description {
    margin-bottom: var(--space-6);
    opacity: 0.9;
    line-height: 1.6;
}

.option-card .btn {
    background: white;
    color: var(--primary-color);
}

.option-card .btn:hover {
    background: var(--gray-100);
}

/* Footer */
.footer {
    background: var(--gray-900);
    color: white;
    padding: var(--space-16) 0 var(--space-8);
}

.footer-content {
    display: grid;
    grid-template-columns: 1fr 2fr;
    gap: var(--space-12);
    margin-bottom: var(--space-8);
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    font-weight: 700;
    font-size: 1.25rem;
    margin-bottom: var(--space-4);
}

.footer-description {
    color: var(--gray-400);
    line-height: 1.6;
}

.footer-links {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--space-8);
}

.link-title {
    font-weight: 600;
    margin-bottom: var(--space-4);
}

.footer-link {
    display: block;
    color: var(--gray-400);
    text-decoration: none;
    margin-bottom: var(--space-2);
    transition: color var(--transition-normal);
}

.footer-link:hover {
    color: white;
}

.footer-bottom {
    border-top: 1px solid var(--gray-800);
    padding-top: var(--space-6);
    text-align: center;
    color: var(--gray-400);
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 0 var(--space-4);
    }
    
    .nav {
        display: none;
    }
    
    .nav-toggle {
        display: flex;
    }
    
    .hero-stats {
        flex-direction: column;
        gap: var(--space-6);
    }
    
    .hero-actions {
        flex-direction: column;
        align-items: center;
    }
    
    .chapter-card {
        flex-direction: column;
        text-align: center;
    }
    
    .chapter-number {
        align-self: center;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
        gap: var(--space-8);
    }
    
    .start-options {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .features-grid,
    .demo-grid {
        grid-template-columns: 1fr;
    }
    
    .hero-badge {
        font-size: 0.75rem;
        padding: var(--space-1) var(--space-3);
    }
    
    .hero-description {
        font-size: 1rem;
    }
}