/* ========================================
   Linear Style CSS Variables & Base Styles
   Modern, Minimal, Beautiful
======================================== */

/* CSS Variables - Light Mode (Default) */
:root {
  /* Primary Colors - Linear Style */
  --primary: #5E6AD2;
  --primary-hover: #4F5AC9;
  --primary-light: #EBECFB;
  
  /* Background Colors */
  --bg-primary: #FFFFFF;
  --bg-secondary: #F7F7F8;
  --bg-tertiary: #F0F0F2;
  
  /* Text Colors */
  --text-primary: #1A1A2E;
  --text-secondary: #5F5F72;
  --text-tertiary: #9595A6;
  --text-inverse: #FFFFFF;
  
  /* Border Colors */
  --border-light: #E8E8EC;
  --border-default: #D8D8DE;
  
  /* Shadow - Subtle & Soft */
  --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.02);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.02);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.04), 0 2px 4px rgba(0, 0, 0, 0.02);
  --shadow-lg: 0 10px 20px rgba(0, 0, 0, 0.06), 0 4px 8px rgba(0, 0, 0, 0.03);
  --shadow-xl: 0 20px 40px rgba(0, 0, 0, 0.08), 0 8px 16px rgba(0, 0, 0, 0.04);
  
  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  
  /* Spacing */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;
  --space-2xl: 48px;
  --space-3xl: 64px;
  
  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, 'Inter', 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', monospace;
  
  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
  --transition-slow: 400ms ease;
  
  /* Focus Ring */
  --focus-ring: 0 0 0 3px rgba(94, 106, 210, 0.2);
}

/* Dark Mode */
[data-theme="dark"] {
  --primary: #8B93E8;
  --primary-hover: #A4ADF5;
  --primary-light: #2A2D42;
  
  --bg-primary: #0D0D14;
  --bg-secondary: #16161E;
  --bg-tertiary: #1E1E2A;
  
  --text-primary: #FFFFFF;
  --text-secondary: #A8A8B8;
  --text-tertiary: #6B6B7D;
  --text-inverse: #0D0D14;
  
  --border-light: #2A2D3A;
  --border-default: #3A3C4A;
  
  --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.2);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3), 0 1px 2px rgba(0, 0, 0, 0.2);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.3), 0 2px 4px rgba(0, 0, 0, 0.2);
  --shadow-lg: 0 10px 20px rgba(0, 0, 0, 0.3), 0 4px 8px rgba(0, 0, 0, 0.2);
  --shadow-xl: 0 20px 40px rgba(0, 0, 0, 0.4), 0 8px 16px rgba(0, 0, 0, 0.2);
  
  --focus-ring: 0 0 0 3px rgba(139, 147, 232, 0.3);
}

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

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  transition: background-color var(--transition-normal), color var(--transition-normal);
}

a {
  color: inherit;
  text-decoration: none;
}

img {
  max-width: 100%;
  height: auto;
}

/* Container */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  letter-spacing: -0.02em;
}

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

p {
  color: var(--text-secondary);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  font-size: 0.9rem;
  font-weight: 500;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

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

.btn-primary:hover {
  background: var(--primary-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

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

.btn-secondary:hover {
  background: var(--bg-tertiary);
  border-color: var(--border-light);
}

/* Cards */
.card {
  background: var(--bg-primary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  transition: all var(--transition-normal);
}

.card:hover {
  border-color: var(--border-default);
  box-shadow: var(--shadow-lg);
}

/* Theme Toggle */
.theme-toggle {
  position: fixed;
  top: var(--space-lg);
  right: var(--space-lg);
  z-index: 1000;
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-secondary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.theme-toggle:hover {
  background: var(--bg-tertiary);
  transform: scale(1.05);
}

.theme-toggle svg {
  width: 20px;
  height: 20px;
  color: var(--text-secondary);
}

[data-theme="dark"] .theme-toggle .sun { display: block; }
[data-theme="dark"] .theme-toggle .moon { display: none; }
[data-theme="dark"] .theme-toggle .sun { display: none; }
[data-theme="dark"] .theme-toggle .moon { display: block; }

/* Progress Bar */
.progress-bar {
  height: 4px;
  background: var(--bg-tertiary);
  border-radius: 2px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), #8B93E8);
  border-radius: 2px;
  transition: width var(--transition-slow);
}

/* Code Blocks */
.code-block {
  background: var(--bg-secondary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  line-height: 1.6;
  color: var(--text-primary);
}

/* Tables */
table {
  width: 100%;
  border-collapse: collapse;
}

th, td {
  padding: var(--space-md);
  text-align: left;
  border-bottom: 1px solid var(--border-light);
}

th {
  font-weight: 500;
  color: var(--text-secondary);
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

tr:hover td {
  background: var(--bg-secondary);
}

/* Navigation */
.nav-links {
  display: flex;
  gap: var(--space-lg);
}

.nav-link {
  color: var(--text-secondary);
  font-weight: 500;
  padding: var(--space-sm) 0;
  position: relative;
  transition: color var(--transition-fast);
}

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

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 2px;
  background: var(--primary);
  transform: scaleX(0);
  transition: transform var(--transition-fast);
}

.nav-link:hover::after,
.nav-link.active::after {
  transform: scaleX(1);
}

/* Grid */
.grid {
  display: grid;
  gap: var(--space-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: 1024px) {
  .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 640px) {
  .grid-4, .grid-3, .grid-2 { grid-template-columns: 1fr; }
  h1 { font-size: 2rem; }
  h2 { font-size: 1.5rem; }
  .container { padding: 0 var(--space-md); }
  .theme-toggle { top: var(--space-md); right: var(--space-md); }
}

/* Utilities */
.text-center { text-align: center; }
.text-muted { color: var(--text-tertiary); }
.mt-md { margin-top: var(--space-md); }
.mt-lg { margin-top: var(--space-lg); }
.mb-md { margin-bottom: var(--space-md); }
.mb-lg { margin-bottom: var(--space-lg); }
.p-lg { padding: var(--space-lg); }
.p-xl { padding: var(--space-xl); }

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

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

@keyframes slideUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

.animate-fade-in {
  animation: fadeIn var(--transition-normal) ease forwards;
}

.animate-slide-up {
  animation: slideUp var(--transition-slow) ease forwards;
}

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

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

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

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

/* Selection */
::selection {
  background: var(--primary);
  color: var(--text-inverse);
}

/* ========================================
   主页专用样式
   ======================================== */

/* Hero Section */
.hero {
  padding: var(--space-3xl) 0;
  text-align: center;
}

.hero-content {
  max-width: 800px;
  margin: 0 auto;
}

.hero h1 {
  font-size: 3rem;
  margin: var(--space-lg) 0;
  line-height: 1.2;
}

.hero-desc {
  font-size: 1.2rem;
  margin-bottom: var(--space-xl);
  line-height: 1.6;
}

.hero-actions {
  display: flex;
  gap: var(--space-md);
  justify-content: center;
  margin-bottom: var(--space-2xl);
}

/* Badge */
.badge {
  display: inline-block;
  padding: var(--space-sm) var(--space-md);
  background: var(--primary-light);
  color: var(--primary);
  font-size: 0.9rem;
  font-weight: 500;
  border-radius: var(--radius-xl);
}

/* Stats */
.stats {
  display: flex;
  justify-content: center;
  gap: var(--space-2xl);
}

.stat {
  text-align: center;
}

.stat-number {
  display: block;
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--text-primary);
  line-height: 1;
}

.stat-label {
  font-size: 0.9rem;
  color: var(--text-tertiary);
  margin-top: var(--space-sm);
}

/* Progress Card */
.progress-card {
  background: var(--bg-secondary);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-2xl);
}

.progress-info {
  display: flex;
  justify-content: space-between;
  margin-bottom: var(--space-md);
  font-size: 0.9rem;
  color: var(--text-secondary);
}

/* Curriculum Grid */
.curriculum-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-xl);
  margin-top: var(--space-xl);
}

.curriculum-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: all var(--transition-normal);
}

.curriculum-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

.curriculum-card .card-header {
  background: var(--primary);
  color: var(--text-inverse);
  padding: var(--space-lg);
}

.curriculum-card .part-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  opacity: 0.8;
}

.curriculum-card h3 {
  font-size: 1.25rem;
  margin: var(--space-sm) 0;
}

.curriculum-card .part-desc {
  font-size: 0.85rem;
  opacity: 0.8;
}

.curriculum-card .lesson-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.curriculum-card .lesson-list li {
  border-bottom: 1px solid var(--border-light);
}

.curriculum-card .lesson-list li:last-child {
  border-bottom: none;
}

.curriculum-card .lesson-list a {
  display: block;
  padding: var(--space-md) var(--space-lg);
  color: var(--text-secondary);
  font-size: 0.9rem;
  transition: all var(--transition-fast);
}

.curriculum-card .lesson-list a:hover {
  background: var(--bg-secondary);
  color: var(--text-primary);
}

/* Footer */
footer {
  padding: var(--space-2xl) 0;
  text-align: center;
  color: var(--text-tertiary);
  font-size: 0.9rem;
  margin-top: var(--space-2xl);
  border-top: 1px solid var(--border-light);
}

/* Responsive */
@media (max-width: 1024px) {
  .curriculum-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 640px) {
  .hero h1 {
    font-size: 2rem;
  }
  
  .hero-desc {
    font-size: 1rem;
  }
  
  .hero-actions {
    flex-direction: column;
  }
  
  .stats {
    gap: var(--space-lg);
  }
  
  .stat-number {
    font-size: 2rem;
  }
  
  .curriculum-grid {
    grid-template-columns: 1fr;
  }
}

/* ========================================
   课程页面专用样式
   ======================================== */

/* Page Header */
.page-header {
  padding: var(--space-xl) 0;
  border-bottom: 1px solid var(--border-light);
  margin-bottom: var(--space-xl);
}

.back-link {
  display: inline-block;
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-bottom: var(--space-lg);
  transition: color var(--transition-fast);
}

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

.header-content h1 {
  font-size: 2rem;
  margin-bottom: var(--space-sm);
}

.header-content .meta {
  font-size: 0.9rem;
  color: var(--text-tertiary);
}

.progress-info {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-top: var(--space-lg);
  font-size: 0.85rem;
  color: var(--text-tertiary);
}

/* Content */
.content {
  max-width: 800px;
}

.section {
  margin-bottom: var(--space-2xl);
}

.section h2 {
  font-size: 1.5rem;
  margin-bottom: var(--space-lg);
  color: var(--text-primary);
}

.section h3 {
  font-size: 1.15rem;
  margin: var(--space-lg) 0 var(--space-md);
  color: var(--text-primary);
}

.section p {
  margin-bottom: var(--space-md);
  line-height: 1.8;
}

/* Goal List */
.goal-list {
  list-style: none;
  padding: 0;
}

.goal-list li {
  padding: var(--space-sm) 0;
  padding-left: var(--space-lg);
  position: relative;
}

.goal-list li::before {
  content: "→";
  position: absolute;
  left: 0;
  color: var(--primary);
}

/* Info Cards */
.info-cards {
  display: flex;
  gap: var(--space-lg);
  margin: var(--space-xl) 0;
}

.info-card {
  flex: 1;
  background: var(--bg-secondary);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  text-align: center;
}

.info-number {
  display: block;
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--primary);
  margin-bottom: var(--space-xs);
}

.info-label {
  font-size: 0.85rem;
  color: var(--text-tertiary);
}

/* Feature List */
.feature-list {
  list-style: none;
  padding: 0;
}

.feature-list li {
  padding: var(--space-sm) 0;
  padding-left: var(--space-lg);
  position: relative;
}

.feature-list li::before {
  content: "✓";
  position: absolute;
  left: 0;
  color: var(--primary);
}

/* Highlight Box */
.highlight-box {
  background: var(--bg-secondary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  margin: var(--space-lg) 0;
}

.highlight-box h4 {
  margin-bottom: var(--space-md);
  color: var(--primary);
}

.highlight-box ul {
  list-style: none;
  padding: 0;
}

.highlight-box li {
  padding: var(--space-sm) 0;
}

.highlight-box.success {
  background: rgba(104, 211, 145, 0.1);
  border-color: rgba(104, 211, 145, 0.3);
}

.highlight-box.warning {
  background: rgba(246, 173, 85, 0.1);
  border-color: rgba(246, 173, 85, 0.3);
}

.highlight-box.error {
  background: rgba(245, 101, 101, 0.1);
  border-color: rgba(245, 101, 101, 0.3);
}

/* Table */
.table-responsive {
  overflow-x: auto;
  margin: var(--space-lg) 0;
}

/* Tips Box */
.tips-box {
  background: linear-gradient(135deg, rgba(94, 106, 210, 0.1) 0%, rgba(139, 147, 232, 0.1) 100%);
  border: 1px solid rgba(94, 106, 210, 0.2);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  margin: var(--space-lg) 0;
}

.tips-box h4 {
  margin-bottom: var(--space-md);
  color: var(--primary);
}

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

.tips-box li {
  padding: var(--space-sm) 0;
}

/* Exercise List */
.exercise-list {
  padding-left: var(--space-xl);
}

.exercise-list li {
  padding: var(--space-sm) 0;
  color: var(--text-secondary);
}

/* Navigation */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  padding: var(--space-xl) 0;
  border-top: 1px solid var(--border-light);
  margin-top: var(--space-xl);
}

/* 404 Page */
.error-container {
  text-align: center;
  padding: var(--space-3xl) 0;
}

.error-container h1 {
  font-size: 6rem;
  color: var(--primary);
  margin-bottom: var(--space-lg);
}

.error-container p {
  font-size: 1.25rem;
  margin-bottom: var(--space-xl);
}

.error-container .btn {
  margin-top: var(--space-lg);
}