/* ============================================
   Interactive C++ Learning Platform
   Modern Design System with Glassmorphism
   ============================================ */

/* ============================================
   CSS Variables & Design Tokens
   ============================================ */
:root {
    /* Color Palette - Light Mode */
    --primary-color: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --secondary-color: #ec4899;
    --accent-color: #14b8a6;
    
    /* Backgrounds */
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    --bg-glass: rgba(255, 255, 255, 0.7);
    
    /* Text Colors */
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-tertiary: #94a3b8;
    --text-inverse: #ffffff;
    
    /* Borders & Shadows */
    --border-color: #e2e8f0;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    --shadow-glow: 0 0 20px rgba(99, 102, 241, 0.3);
    
    /* Gradients */
    --gradient-primary: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --gradient-secondary: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    --gradient-accent: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    --gradient-success: linear-gradient(135deg, #43e97b 0%, #38f9d7 100%);
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-2xl: 1.5rem;
    
    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-code: 'Fira Code', 'Courier New', monospace;
    
    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 250ms ease-in-out;
    --transition-slow: 350ms ease-in-out;
}

/* Dark Mode Variables */
[data-theme="dark"] {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --bg-glass: rgba(30, 41, 59, 0.7);
    
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --text-tertiary: #64748b;
    --text-inverse: #0f172a;
    
    --border-color: #334155;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.6);
}

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

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

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

/* Animated Background */
body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--gradient-primary);
    opacity: 0.03;
    z-index: -1;
    pointer-events: none;
}

[data-theme="dark"] body::before {
    opacity: 0.05;
}

/* ============================================
   Typography
   ============================================ */
h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.75rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1rem; }

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

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

a:hover {
    color: var(--primary-dark);
}

code {
    font-family: var(--font-code);
    background: var(--bg-tertiary);
    padding: 0.125rem 0.375rem;
    border-radius: var(--radius-sm);
    font-size: 0.875em;
}

/* ============================================
   Layout Components
   ============================================ */
.container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.container-fluid {
    width: 100%;
    padding: 0 var(--spacing-lg);
}

/* Grid System */
.grid {
    display: grid;
    gap: var(--spacing-lg);
}

.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

@media (max-width: 768px) {
    .grid-2, .grid-3, .grid-4 {
        grid-template-columns: 1fr;
    }
}

/* Flex Utilities */
.flex {
    display: flex;
}

.flex-center {
    display: flex;
    align-items: center;
    justify-content: center;
}

.flex-between {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.flex-column {
    display: flex;
    flex-direction: column;
}

/* ============================================
   Glassmorphism Cards
   ============================================ */
.glass-card {
    background: var(--bg-glass);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-lg);
    transition: transform var(--transition-base), box-shadow var(--transition-base);
}

.glass-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
}

[data-theme="dark"] .glass-card {
    border: 1px solid rgba(255, 255, 255, 0.1);
}

/* ============================================
   Buttons
   ============================================ */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: var(--radius-lg);
    font-family: var(--font-primary);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-base);
    text-decoration: none;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.3);
    transform: translate(-50%, -50%);
    transition: width var(--transition-slow), height var(--transition-slow);
}

.btn:hover::before {
    width: 300px;
    height: 300px;
}

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

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

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

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

.btn-outline {
    background: transparent;
    border: 2px solid var(--primary-color);
    color: var(--primary-color);
}

.btn-outline:hover {
    background: var(--primary-color);
    color: var(--text-inverse);
}

/* ============================================
   Header & Navigation
   ============================================ */
.header {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: var(--bg-glass);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    padding: var(--spacing-md) 0;
    box-shadow: var(--shadow-sm);
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--spacing-lg);
}

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

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

.nav-link {
    color: var(--text-secondary);
    font-weight: 500;
    padding: 0.5rem 1rem;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.nav-link:hover,
.nav-link.active {
    color: var(--primary-color);
    background: var(--bg-tertiary);
}

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

.hero-title {
    font-size: 3.5rem;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-lg);
    animation: fadeInUp 0.8s ease-out;
}

.hero-subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto var(--spacing-xl);
    animation: fadeInUp 0.8s ease-out 0.2s both;
}

/* ============================================
   Chapter Cards
   ============================================ */
.chapter-card {
    position: relative;
    background: var(--bg-glass);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    transition: all var(--transition-base);
    cursor: pointer;
    overflow: hidden;
}

.chapter-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 4px;
    background: var(--gradient-primary);
    transform: scaleX(0);
    transform-origin: left;
    transition: transform var(--transition-base);
}

.chapter-card:hover::before {
    transform: scaleX(1);
}

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

.chapter-number {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 3rem;
    height: 3rem;
    background: var(--gradient-primary);
    color: var(--text-inverse);
    border-radius: 50%;
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: var(--spacing-md);
}

.chapter-title {
    font-size: 1.5rem;
    margin-bottom: var(--spacing-sm);
}

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

.chapter-progress {
    width: 100%;
    height: 6px;
    background: var(--bg-tertiary);
    border-radius: 999px;
    overflow: hidden;
    margin-top: var(--spacing-md);
}

.chapter-progress-bar {
    height: 100%;
    background: var(--gradient-primary);
    border-radius: 999px;
    transition: width var(--transition-slow);
}

/* ============================================
   Code Editor Styles
   ============================================ */
.code-editor-container {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    overflow: hidden;
    margin: var(--spacing-lg) 0;
}

.code-editor-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md);
    background: var(--bg-tertiary);
    border-bottom: 1px solid var(--border-color);
}

.code-editor-title {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-secondary);
}

.code-editor-actions {
    display: flex;
    gap: var(--spacing-sm);
}

.code-editor {
    position: relative;
    font-family: var(--font-code);
    font-size: 0.875rem;
    line-height: 1.6;
    overflow-x: auto;
}

.code-output {
    background: #1e1e1e;
    color: #d4d4d4;
    padding: var(--spacing-md);
    font-family: var(--font-code);
    font-size: 0.875rem;
    min-height: 100px;
    border-top: 1px solid var(--border-color);
}

/* ============================================
   Theme Toggle
   ============================================ */
.theme-toggle {
    position: relative;
    width: 60px;
    height: 30px;
    background: var(--bg-tertiary);
    border-radius: 999px;
    cursor: pointer;
    transition: background var(--transition-base);
    border: 2px solid var(--border-color);
}

.theme-toggle-slider {
    position: absolute;
    top: 2px;
    left: 2px;
    width: 22px;
    height: 22px;
    background: var(--primary-color);
    border-radius: 50%;
    transition: transform var(--transition-base);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
}

[data-theme="dark"] .theme-toggle-slider {
    transform: translateX(30px);
}

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

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

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

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.animate-fadeIn {
    animation: fadeIn 0.5s ease-out;
}

.animate-fadeInUp {
    animation: fadeInUp 0.6s ease-out;
}

.animate-slideInRight {
    animation: slideInRight 0.6s ease-out;
}

/* ============================================
   Utility Classes
   ============================================ */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-md); }
.mt-3 { margin-top: var(--spacing-lg); }
.mt-4 { margin-top: var(--spacing-xl); }

.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-md); }
.mb-3 { margin-bottom: var(--spacing-lg); }
.mb-4 { margin-bottom: var(--spacing-xl); }

.p-1 { padding: var(--spacing-sm); }
.p-2 { padding: var(--spacing-md); }
.p-3 { padding: var(--spacing-lg); }
.p-4 { padding: var(--spacing-xl); }

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 768px) {
    html { font-size: 14px; }
    
    .hero-title { font-size: 2.5rem; }
    .hero-subtitle { font-size: 1rem; }
    
    .nav-links {
        position: fixed;
        top: 70px;
        left: 0;
        right: 0;
        background: var(--bg-glass);
        backdrop-filter: blur(10px);
        flex-direction: column;
        padding: var(--spacing-lg);
        transform: translateY(-100%);
        opacity: 0;
        transition: all var(--transition-base);
    }
    
    .nav-links.active {
        transform: translateY(0);
        opacity: 1;
    }
}

/* ============================================
   Custom Scrollbar
   ============================================ */
::-webkit-scrollbar {
    width: 10px;
    height: 10px;
}

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

::-webkit-scrollbar-thumb {
    background: var(--primary-color);
    border-radius: 999px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--primary-dark);
}

/* ============================================
   Loading States
   ============================================ */
.loading {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 3px solid var(--bg-tertiary);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}