@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

/* CSS Variables */
:root {
    --primary-color: #2563eb;
    --secondary-color: #64748b;
    --accent-color: #f59e0b;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --error-color: #ef4444;
    
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    
    --border-color: #e2e8f0;
    --border-light: #f1f5f9;
    
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
    
    --radius-sm: 0.25rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
}

/* Dark Mode Variables */
[data-theme="dark"] {
    --text-primary: #f8fafc;
    --text-secondary: #cbd5e1;
    --text-muted: #64748b;
    
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    
    --border-color: #334155;
    --border-light: #475569;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', sans-serif;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-secondary);
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Smooth scrolling */
html {
    scroll-behavior: smooth;
}

/* Header */
.header {
    background-color: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: var(--shadow-sm);
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 4rem;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.logo-icon {
    font-size: 2rem;
}

.logo h1 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
}

.header-controls {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.theme-btn,
.mobile-menu-btn {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--spacing-sm);
    cursor: pointer;
    font-size: 1.25rem;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 2.5rem;
    height: 2.5rem;
}

.theme-btn:hover,
.mobile-menu-btn:hover {
    background: var(--border-color);
    transform: translateY(-1px);
}

.mobile-menu-btn {
    display: none;
}

/* Main Container */
.main-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-xl) var(--spacing-md);
    display: grid;
    grid-template-columns: 250px 1fr;
    gap: var(--spacing-2xl);
    align-items: start;
}

/* Sidebar */
.sidebar {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    position: sticky;
    top: 6rem;
}

.sidebar h2 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
}

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

.nav-list li {
    margin-bottom: var(--spacing-sm);
}

.nav-btn {
    width: 100%;
    background: none;
    border: none;
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-secondary);
    transition: all 0.2s ease;
    text-align: left;
}

.nav-btn:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    transform: translateX(4px);
}

.nav-btn.active {
    background: linear-gradient(135deg, var(--primary-color), #3b82f6);
    color: white;
    box-shadow: var(--shadow-md);
}

.nav-btn.active:hover {
    transform: translateX(4px) translateY(-1px);
}

.nav-icon {
    font-size: 1.25rem;
}

/* Main Content */
.main-content {
    min-height: 100vh;
}

/* Hero Section */
.hero {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    padding: var(--spacing-2xl) 0;
}

.hero-title {
    font-size: clamp(2.5rem, 5vw, 4rem);
    font-weight: 800;
    line-height: 1.1;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.hero-subtitle {
    display: block;
    background: linear-gradient(135deg, #ff6b35 0%, #f7931e 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    font-size: clamp(2rem, 4vw, 3rem);
}

.hero-description {
    font-size: 1.25rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
    line-height: 1.6;
}

/* Feature Cards */
.feature-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-2xl);
}

.feature-card {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    text-align: center;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-md);
    border: 1px solid var(--border-color);
}

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

.feature-icon {
    width: 4rem;
    height: 4rem;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    margin: 0 auto var(--spacing-md);
    color: white;
}

.html-gradient {
    background: linear-gradient(135deg, #ff6b35 0%, #f7931e 100%);
}

.css-gradient {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.js-gradient {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
}

.api-gradient {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
}

.feature-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.feature-card p {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* Content Sections */
.content-section {
    display: none;
}

.content-section.active {
    display: block;
    animation: fadeInUp 0.6s ease-out;
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Section Headers */
.section-header {
    background: linear-gradient(135deg, #ff6b35 0%, #f7931e 100%);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    margin-bottom: var(--spacing-2xl);
    color: white;
    display: flex;
    align-items: center;
    gap: var(--spacing-lg);
}

.section-header.css-gradient {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.section-header.js-gradient {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
}

.section-header.api-gradient {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
}

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

.section-header h2 {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
}

.section-header p {
    font-size: 1rem;
    opacity: 0.9;
}

/* Topics */
.topics {
    display: grid;
    gap: var(--spacing-2xl);
}

/* Topic Cards */
.topic-card {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
}

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

.topic-card h3 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.topic-card > p {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-xl);
    font-size: 1rem;
}

/* Examples */
.example {
    margin-bottom: var(--spacing-xl);
}

.example h4 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

/* Code Blocks */
.code-block {
    position: relative;
    background: #1e293b;
    border-radius: var(--radius-lg);
    overflow: hidden;
    margin-bottom: var(--spacing-md);
    box-shadow: var(--shadow-md);
}

.copy-btn {
    position: absolute;
    top: var(--spacing-md);
    right: var(--spacing-md);
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: var(--radius-sm);
    color: white;
    padding: var(--spacing-sm) var(--spacing-md);
    cursor: pointer;
    font-size: 0.875rem;
    transition: all 0.2s ease;
    z-index: 10;
}

.copy-btn:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: translateY(-1px);
}

.code-block pre {
    margin: 0;
    padding: var(--spacing-xl);
    padding-top: 3.5rem;
    overflow-x: auto;
    font-family: 'SF Mono', 'Monaco', 'Inconsolata', 'Roboto Mono', 'Courier New', monospace;
    font-size: 0.875rem;
    line-height: 1.6;
    color: #e2e8f0;
}

.code-block code {
    font-family: inherit;
}

/* Explanations */
.explanation {
    background: #dbeafe;
    border: 1px solid #93c5fd;
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    font-size: 0.875rem;
    line-height: 1.6;
    color: #1e40af;
}

[data-theme="dark"] .explanation {
    background: rgba(59, 130, 246, 0.1);
    border-color: rgba(59, 130, 246, 0.3);
    color: #93c5fd;
}

/* Tips */
.tips {
    background: #fef3c7;
    border: 1px solid #fbbf24;
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

[data-theme="dark"] .tips {
    background: rgba(245, 158, 11, 0.1);
    border-color: rgba(245, 158, 11, 0.3);
}

.tips h4 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: #92400e;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

[data-theme="dark"] .tips h4 {
    color: #fbbf24;
}

.tips ul {
    list-style: none;
    padding-left: 0;
}

.tips li {
    position: relative;
    padding-left: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
    font-size: 0.875rem;
    line-height: 1.5;
    color: #92400e;
}

[data-theme="dark"] .tips li {
    color: #fcd34d;
}

.tips li::before {
    content: '•';
    position: absolute;
    left: 0;
    color: #f59e0b;
    font-weight: bold;
}

/* Demo Container */
.demo-container {
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin: var(--spacing-lg) 0;
}

.demo-button {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    cursor: pointer;
    margin-right: var(--spacing-sm);
    margin-bottom: var(--spacing-sm);
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.2s ease;
}

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

.demo-button:nth-child(2) {
    background: var(--success-color);
}

.demo-button:nth-child(3) {
    background: var(--warning-color);
}

.demo-output {
    margin-top: var(--spacing-md);
    padding: var(--spacing-md);
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    min-height: 60px;
    font-size: 0.875rem;
}

/* Responsive Design */
@media (max-width: 1024px) {
    .main-container {
        grid-template-columns: 200px 1fr;
        gap: var(--spacing-lg);
    }
    
    .sidebar {
        padding: var(--spacing-lg);
    }
}

@media (max-width: 768px) {
    .mobile-menu-btn {
        display: flex;
    }
    
    .main-container {
        grid-template-columns: 1fr;
        padding: var(--spacing-lg) var(--spacing-md);
    }
    
    .sidebar {
        display: none;
        position: fixed;
        top: 4rem;
        left: 0;
        right: 0;
        z-index: 999;
        border-radius: 0;
        box-shadow: var(--shadow-xl);
    }
    
    .sidebar.active {
        display: block;
        animation: slideDown 0.3s ease-out;
    }
    
    @keyframes slideDown {
        from {
            opacity: 0;
            transform: translateY(-20px);
        }
        to {
            opacity: 1;
            transform: translateY(0);
        }
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .hero-subtitle {
        font-size: 2rem;
    }
    
    .hero-description {
        font-size: 1.125rem;
    }
    
    .feature-cards {
        grid-template-columns: 1fr;
    }
    
    .section-header {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-md);
    }
    
    .section-icon {
        font-size: 2.5rem;
    }
    
    .topic-card {
        padding: var(--spacing-lg);
    }
    
    .code-block pre {
        padding: var(--spacing-lg);
        padding-top: 3rem;
        font-size: 0.8rem;
    }
}

@media (max-width: 480px) {
    .header-content {
        padding: 0 var(--spacing-sm);
    }
    
    .main-container {
        padding: var(--spacing-md) var(--spacing-sm);
    }
    
    .hero {
        padding: var(--spacing-lg) 0;
    }
    
    .section-header {
        padding: var(--spacing-lg);
    }
    
    .topic-card {
        padding: var(--spacing-md);
    }
    
    .demo-container {
        padding: var(--spacing-md);
    }
    
    .demo-button {
        display: block;
        width: 100%;
        margin-right: 0;
        margin-bottom: var(--spacing-sm);
    }
}

/* Custom Scrollbar */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-tertiary);
}

::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* Focus Styles */
button:focus-visible,
.nav-btn:focus-visible {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* Print Styles */
@media print {
    .header,
    .sidebar,
    .copy-btn {
        display: none;
    }
    
    .main-container {
        grid-template-columns: 1fr;
        max-width: none;
        margin: 0;
        padding: 0;
    }
    
    .content-section {
        display: block !important;
        page-break-before: always;
    }
    
    .content-section:first-child {
        page-break-before: auto;
    }
}