/* CSS Custom Properties for consistent theming */
:root {
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --secondary-gradient: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    --accent-gradient: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    --dark-gradient: linear-gradient(135deg, #2c3e50 0%, #34495e 100%);
    
    --primary-color: #667eea;
    --secondary-color: #764ba2;
    --accent-color: #4facfe;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --error-color: #ef4444;
    
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-muted: #718096;
    --text-light: #a0aec0;
    
    --bg-primary: #ffffff;
    --bg-secondary: #f7fafc;
    --bg-tertiary: #edf2f7;
    --bg-overlay: rgba(0, 0, 0, 0.5);
    
    --border-color: #e2e8f0;
    --border-light: #f1f5f9;
    
    --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);
    
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    --transition-fast: all 0.15s ease;
    --transition-normal: all 0.3s ease;
    --transition-slow: all 0.5s ease;
    
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
    
    --sidebar-width: 320px;
    --header-height: 70px;
}

/* Global Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

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

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: 600;
    line-height: 1.2;
    margin-bottom: 1rem;
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.25rem; }
h5 { font-size: 1.125rem; }
h6 { font-size: 1rem; }

p {
    margin-bottom: 1rem;
    line-height: 1.7;
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: var(--transition-fast);
}

a:hover {
    color: var(--secondary-color);
}

/* Layout */
.layout {
    display: flex;
    min-height: 100vh;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
}

/* Sidebar Toggle (Hidden Checkbox) */
.sidebar-toggle {
    display: none;
}

/* Sidebar Styles */
.sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: var(--sidebar-width);
    height: 100vh;
    background: linear-gradient(180deg, #ffffff 0%, #f8fafc 100%);
    border-right: 1px solid var(--border-color);
    transform: translateX(-100%);
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 1000;
    overflow-y: auto;
    box-shadow: var(--shadow-xl);
}

.sidebar-toggle:checked ~ .layout .sidebar {
    transform: translateX(0);
}

.sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1.5rem 2rem;
    border-bottom: 1px solid var(--border-light);
    background: var(--primary-gradient);
    color: white;
    position: sticky;
    top: 0;
    z-index: 100;
}

.sidebar-header h2 {
    font-size: 1.25rem;
    font-weight: 600;
    margin: 0;
}

.close-btn {
    font-size: 1.5rem;
    cursor: pointer;
    color: white;
    opacity: 0.8;
    transition: var(--transition-fast);
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-sm);
}

.close-btn:hover {
    opacity: 1;
    background: rgba(255, 255, 255, 0.1);
}

.sidebar-content {
    padding: 2rem 0;
}

.topic-section {
    margin-bottom: 2rem;
}

.topic-section h3 {
    padding: 0 2rem 1rem;
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    border-bottom: 1px solid var(--border-light);
    margin-bottom: 1rem;
}

.topic-list {
    list-style: none;
}

.topic-list li {
    margin-bottom: 0.25rem;
}

.topic-list a {
    display: block;
    padding: 0.75rem 2rem;
    color: var(--text-secondary);
    font-weight: 400;
    transition: var(--transition-fast);
    border-left: 3px solid transparent;
    position: relative;
}

.topic-list a:hover {
    color: var(--primary-color);
    background: linear-gradient(90deg, rgba(102, 126, 234, 0.1) 0%, transparent 100%);
    border-left-color: var(--primary-color);
    transform: translateX(4px);
}

.topic-list a.active {
    color: var(--primary-color);
    background: linear-gradient(90deg, rgba(102, 126, 234, 0.15) 0%, transparent 100%);
    border-left-color: var(--primary-color);
    font-weight: 500;
}

/* Main Content */
.main-content {
    flex: 1;
    margin-left: 0;
    transition: margin-left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.header {
    height: var(--header-height);
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    padding: 0 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-sm);
}

.menu-btn {
    display: flex;
    flex-direction: column;
    cursor: pointer;
    padding: 0.5rem;
    margin-right: 1rem;
    border-radius: var(--radius-sm);
    transition: var(--transition-fast);
}

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

.menu-btn span {
    width: 24px;
    height: 3px;
    background: var(--text-primary);
    margin: 2px 0;
    transition: var(--transition-fast);
    border-radius: 2px;
}

.logo h1 {
    font-size: 1.5rem;
    font-weight: 700;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin: 0;
}

/* Hero Section */
.hero {
    padding: 4rem 2rem;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23ffffff' fill-opacity='0.05'%3E%3Ccircle cx='30' cy='30' r='2'/%3E%3C/g%3E%3C/g%3E%3C/svg%3E") repeat;
    pointer-events: none;
}

.hero-content {
    max-width: 1200px;
    margin: 0 auto;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    align-items: center;
    position: relative;
    z-index: 1;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 700;
    line-height: 1.1;
    margin-bottom: 1.5rem;
}

.gradient-text {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-description {
    font-size: 1.125rem;
    line-height: 1.7;
    color: rgba(255, 255, 255, 0.9);
    margin-bottom: 2rem;
}

.hero-stats {
    display: flex;
    gap: 2rem;
}

.stat {
    text-align: center;
}

.stat-number {
    font-size: 2.5rem;
    font-weight: 700;
    line-height: 1;
    margin-bottom: 0.5rem;
}

.stat-label {
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.8);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Code Window */
.code-window {
    background: #1a202c;
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-xl);
    transform: rotate(2deg);
    transition: var(--transition-normal);
}

.code-window:hover {
    transform: rotate(0deg) scale(1.02);
}

.window-header {
    background: #2d3748;
    padding: 1rem;
    display: flex;
    align-items: center;
    gap: 1rem;
}

.window-controls {
    display: flex;
    gap: 0.5rem;
}

.control {
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.control.red { background: #ef4444; }
.control.yellow { background: #f59e0b; }
.control.green { background: #10b981; }

.window-title {
    color: #a0aec0;
    font-family: var(--font-mono);
    font-size: 0.875rem;
}

.code-content {
    padding: 1.5rem;
    font-family: var(--font-mono);
    font-size: 0.875rem;
    line-height: 1.6;
}

.code-line {
    margin-bottom: 0.25rem;
}

.indent { padding-left: 1rem; }
.indent2 { padding-left: 2rem; }

.tag { color: #81c784; }
.attr { color: #ffb74d; }
.string { color: #f06292; }

/* Course Overview */
.course-overview {
    padding: 6rem 0;
    background: var(--bg-primary);
}

.section-title {
    text-align: center;
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.section-description {
    text-align: center;
    font-size: 1.125rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto 3rem;
}

.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(400px, 1fr));
    gap: 2rem;
    margin-top: 3rem;
}

.course-card {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: 2.5rem;
    text-align: center;
    box-shadow: var(--shadow-lg);
    transition: var(--transition-normal);
    border: 1px solid var(--border-light);
    position: relative;
    overflow: hidden;
}

.course-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: var(--primary-gradient);
}

.course-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-xl);
}

.html-card::before {
    background: linear-gradient(135deg, #e65100 0%, #ff9800 100%);
}

.css-card::before {
    background: linear-gradient(135deg, #1565c0 0%, #42a5f5 100%);
}

.course-icon {
    width: 80px;
    height: 80px;
    margin: 0 auto 1.5rem;
    background: var(--primary-gradient);
    border-radius: var(--radius-xl);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
}

.html-card .course-icon {
    background: linear-gradient(135deg, #e65100 0%, #ff9800 100%);
}

.css-card .course-icon {
    background: linear-gradient(135deg, #1565c0 0%, #42a5f5 100%);
}

.course-icon svg {
    width: 40px;
    height: 40px;
}

.course-card h3 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.course-card p {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 1.5rem;
}

.course-stats {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-bottom: 2rem;
}

.course-stats span {
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    padding: 0.375rem 0.75rem;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 500;
}

.course-btn {
    display: inline-block;
    background: var(--primary-gradient);
    color: white;
    padding: 0.875rem 2rem;
    border-radius: var(--radius-lg);
    font-weight: 600;
    transition: var(--transition-normal);
    box-shadow: var(--shadow-md);
}

.html-card .course-btn {
    background: linear-gradient(135deg, #e65100 0%, #ff9800 100%);
}

.css-card .course-btn {
    background: linear-gradient(135deg, #1565c0 0%, #42a5f5 100%);
}

.course-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
    color: white;
}

/* Features Section */
.features {
    padding: 6rem 0;
    background: var(--bg-secondary);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin-top: 3rem;
}

.feature-card {
    background: var(--bg-primary);
    padding: 2rem;
    border-radius: var(--radius-lg);
    text-align: center;
    box-shadow: var(--shadow-md);
    transition: var(--transition-normal);
    border: 1px solid var(--border-light);
}

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

.feature-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.feature-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.feature-card p {
    color: var(--text-secondary);
    line-height: 1.6;
    margin: 0;
}

/* Footer */
.footer {
    background: var(--dark-gradient);
    color: white;
    padding: 3rem 0 1rem;
    margin-top: auto;
}

.footer-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 3rem;
    margin-bottom: 2rem;
}

.footer-brand h3 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
}

.footer-brand p {
    color: rgba(255, 255, 255, 0.8);
    line-height: 1.6;
}

.footer-links {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
}

.footer-section h4 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: 0.5rem;
}

.footer-section ul li a {
    color: rgba(255, 255, 255, 0.7);
    transition: var(--transition-fast);
}

.footer-section ul li a:hover {
    color: white;
}

.footer-bottom {
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    padding-top: 2rem;
    text-align: center;
    color: rgba(255, 255, 255, 0.6);
}

/* Overlay for mobile */
.overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--bg-overlay);
    opacity: 0;
    visibility: hidden;
    transition: var(--transition-normal);
    z-index: 999;
}

.sidebar-toggle:checked ~ .overlay {
    opacity: 1;
    visibility: visible;
}

/* Topic Page Styles */
.topic-header {
    background: var(--primary-gradient);
    color: white;
    padding: 3rem 0;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.topic-header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: url("data:image/svg+xml,%3Csvg width='40' height='40' viewBox='0 0 40 40' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='%23ffffff' fill-opacity='0.03'%3E%3Cpath d='M20 20c0 11.046-8.954 20-20 20s-20-8.954-20-20 8.954-20 20-20 20 8.954 20 20zm-20-8c-4.418 0-8 3.582-8 8s3.582 8 8 8 8-3.582 8-8-3.582-8-8-8z'/%3E%3C/g%3E%3C/svg%3E") repeat;
}

.topic-title {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: 1rem;
    position: relative;
    z-index: 1;
}

.topic-description {
    font-size: 1.25rem;
    color: rgba(255, 255, 255, 0.9);
    max-width: 600px;
    margin: 0 auto;
    position: relative;
    z-index: 1;
}

.topic-content {
    max-width: 800px;
    margin: 0 auto;
    padding: 3rem 2rem;
}

.content-section {
    margin-bottom: 3rem;
}

.content-section h2 {
    font-size: 1.75rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
    border-left: 4px solid var(--primary-color);
    padding-left: 1rem;
}

.content-section h3 {
    font-size: 1.375rem;
    font-weight: 600;
    margin: 2rem 0 1rem;
    color: var(--text-primary);
}

.code-block {
    background: #1a202c;
    color: #e2e8f0;
    padding: 2rem;
    border-radius: var(--radius-lg);
    font-family: var(--font-mono);
    font-size: 0.875rem;
    line-height: 1.6;
    margin: 1.5rem 0;
    overflow-x: auto;
    box-shadow: var(--shadow-md);
    border: 1px solid #2d3748;
}

.code-block pre {
    margin: 0;
    white-space: pre-wrap;
}

.example-box {
    background: var(--bg-primary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 2rem;
    margin: 1.5rem 0;
    box-shadow: var(--shadow-sm);
}

.example-title {
    font-weight: 600;
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.125rem;
}

.highlight-box {
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.1) 0%, rgba(118, 75, 162, 0.1) 100%);
    border-left: 4px solid var(--primary-color);
    padding: 1.5rem;
    border-radius: var(--radius-md);
    margin: 1.5rem 0;
}

.highlight-box h4 {
    color: var(--primary-color);
    font-weight: 600;
    margin-bottom: 0.75rem;
}

.navigation-controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 2rem 0;
    border-top: 1px solid var(--border-color);
    margin-top: 3rem;
}

.nav-btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    background: var(--primary-gradient);
    color: white;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-lg);
    font-weight: 500;
    transition: var(--transition-normal);
    box-shadow: var(--shadow-md);
}

.nav-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
    color: white;
}

.nav-btn.disabled {
    background: var(--bg-tertiary);
    color: var(--text-muted);
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

/* Responsive Design */
@media (max-width: 1024px) {
    .hero-content {
        grid-template-columns: 1fr;
        gap: 2rem;
        text-align: center;
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .course-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
        gap: 2rem;
    }
}

@media (max-width: 768px) {
    :root {
        --sidebar-width: 280px;
    }
    
    .container {
        padding: 0 1rem;
    }
    
    .hero {
        padding: 2rem 1rem;
    }
    
    .hero-title {
        font-size: 2rem;
    }
    
    .hero-stats {
        justify-content: center;
        gap: 1rem;
    }
    
    .stat-number {
        font-size: 2rem;
    }
    
    .course-grid {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
    
    .course-card {
        padding: 2rem;
    }
    
    .features-grid {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
    
    .topic-title {
        font-size: 2rem;
    }
    
    .topic-content {
        padding: 2rem 1rem;
    }
    
    .navigation-controls {
        flex-direction: column;
        gap: 1rem;
    }
    
    .footer-links {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 1.75rem;
    }
    
    .section-title {
        font-size: 2rem;
    }
    
    .topic-title {
        font-size: 1.75rem;
    }
    
    .code-block {
        padding: 1rem;
        font-size: 0.8rem;
    }
    
    .example-box {
        padding: 1rem;
    }
}

/* Print Styles */
@media print {
    .sidebar,
    .header,
    .navigation-controls,
    .footer {
        display: none;
    }
    
    .main-content {
        margin-left: 0;
    }
    
    .topic-content {
        max-width: none;
        padding: 0;
    }
    
    .code-block {
        background: #f8f9fa;
        color: #1a202c;
        border: 1px solid #e2e8f0;
    }
}

/* Animation Keyframes */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeIn 0.6s ease-out;
}

/* Focus Styles for Accessibility */
*:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

button:focus,
a:focus,
input:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* High Contrast Mode Support */
@media (prefers-contrast: high) {
    :root {
        --text-primary: #000000;
        --text-secondary: #000000;
        --border-color: #000000;
        --bg-primary: #ffffff;
        --bg-secondary: #ffffff;
    }
}

/* Reduced Motion Support */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}