/* ============================================
   OceanBase SQL 调优学习网站 - 极简设计系统
   ============================================ */

/* CSS Variables */
:root {
  --color-primary: #10B981;
  --color-primary-light: #34D399;
  --color-secondary: #059669;
  --color-accent: #FBBF24;
  --color-background: #F9FAFB;
  --color-surface: #FFFFFF;
  --color-text: #1F2937;
  --color-text-muted: #6B7280;
  --color-border: #E5E7EB;
  --color-success: #10B981;
  --color-error: #EF4444;
  
  --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'Courier New', Consolas, Monaco, monospace;
  
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  
  --shadow-sm: 0 1px 2px 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);
  
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 350ms ease;
}

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

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

body {
  font-family: var(--font-family);
  background-color: var(--color-background);
  color: var(--color-text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  color: var(--color-text);
}

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

p {
  margin-bottom: 1rem;
  color: var(--color-text-muted);
}

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

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

/* Layout */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

.section {
  padding: 4rem 0;
}

/* Header & Navigation */
.header {
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 64px;
}

.nav-brand {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--color-text);
}

.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  color: var(--color-text-muted);
  font-weight: 500;
  font-size: 0.875rem;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-primary);
}

/* Hero Section */
.hero {
  padding: 6rem 0 4rem;
  text-align: center;
  background: linear-gradient(135deg, var(--color-surface) 0%, var(--color-background) 100%);
}

.hero-title {
  font-size: 3rem;
  font-weight: 700;
  line-height: 1.2;
  margin-bottom: 1.5rem;
  background: linear-gradient(135deg, var(--color-text) 0%, var(--color-primary) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-subtitle {
  font-size: 1.125rem;
  color: var(--color-text-muted);
  max-width: 600px;
  margin: 0 auto 2rem;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  justify-content: center;
  margin-bottom: 3rem;
}

/* Animation Demo */
.hero-animation {
  max-width: 800px;
  margin: 0 auto;
  padding: 2rem;
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  overflow: hidden;
}

.animation-container {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
}

.animation-item {
  padding: 0.75rem 1.25rem;
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
  border-radius: var(--radius-md);
  font-weight: 500;
  font-size: 0.875rem;
  animation: fadeInUp 0.6s ease forwards;
  opacity: 0;
  transform: translateY(20px);
}

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

/* Stats */
.stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 1.5rem;
  max-width: 600px;
  margin: 3rem auto 0;
}

.stat-card {
  text-align: center;
  padding: 1.5rem;
  background: var(--color-surface);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.stat-value {
  font-size: 2rem;
  font-weight: 700;
  color: var(--color-primary);
  display: block;
}

.stat-label {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-top: 0.25rem;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.875rem 1.5rem;
  font-size: 0.9375rem;
  font-weight: 500;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
}

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

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

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

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

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

.btn-accent:hover {
  background: #F59E0B;
  color: var(--color-text);
}

/* Cards */
.card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  transition: all var(--transition-base);
}

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

.card-header {
  padding: 1.5rem;
  border-bottom: 1px solid var(--color-border);
}

.card-body {
  padding: 1.5rem;
}

.card-footer {
  padding: 1rem 1.5rem;
  background: var(--color-background);
  border-top: 1px solid var(--color-border);
}

/* Grid */
.grid {
  display: grid;
  gap: 1.5rem;
}

.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(3, 1fr); }
}

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

/* Flashcard */
.flashcard-container {
  perspective: 1000px;
  max-width: 600px;
  margin: 2rem auto;
}

.flashcard {
  position: relative;
  width: 100%;
  height: 400px;
  transform-style: preserve-3d;
  transition: transform 0.6s;
  cursor: pointer;
}

.flashcard.flipped {
  transform: rotateY(180deg);
}

.flashcard-face {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  background: var(--color-surface);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 2rem;
  text-align: center;
}

.flashcard-back {
  transform: rotateY(180deg);
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
}

.flashcard-back h3,
.flashcard-back p {
  color: white;
}

.flashcard-title {
  font-size: 2rem;
  margin-bottom: 1rem;
}

.flashcard-meta {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Quiz */
.quiz-container {
  max-width: 700px;
  margin: 2rem auto;
}

.quiz-question {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 1.5rem;
  color: var(--color-text);
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.quiz-option {
  padding: 1rem 1.25rem;
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: left;
}

.quiz-option:hover {
  border-color: var(--color-primary);
  background: rgba(16, 185, 129, 0.05);
}

.quiz-option.correct {
  border-color: var(--color-success);
  background: rgba(16, 185, 129, 0.1);
}

.quiz-option.incorrect {
  border-color: var(--color-error);
  background: rgba(239, 68, 68, 0.1);
}

.quiz-option.disabled {
  cursor: not-allowed;
  opacity: 0.7;
}

/* Progress */
.progress-bar {
  width: 100%;
  height: 8px;
  background: var(--color-border);
  border-radius: 4px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  border-radius: 4px;
  transition: width var(--transition-base);
}

.progress-ring {
  transform: rotate(-90deg);
}

.progress-ring-circle {
  transition: stroke-dashoffset var(--transition-base);
}

/* Search */
.search-container {
  position: relative;
  max-width: 500px;
  margin: 0 auto 2rem;
}

.search-input {
  width: 100%;
  padding: 1rem 1rem 1rem 3rem;
  font-size: 1rem;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  transition: border-color var(--transition-fast);
}

.search-input:focus {
  outline: none;
  border-color: var(--color-primary);
}

.search-icon {
  position: absolute;
  left: 1rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--color-text-muted);
}

/* Tags & Filters */
.tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: center;
  margin-bottom: 2rem;
}

.tag {
  padding: 0.5rem 1rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  color: var(--color-text-muted);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.tag:hover,
.tag.active {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

/* Root Card (for index page) */
.root-card {
  padding: 1.5rem;
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-base);
  cursor: pointer;
  border: 2px solid transparent;
}

.root-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
  border-color: var(--color-primary);
}

.root-card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 0.75rem;
}

.root-card-id {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--color-primary);
  background: rgba(16, 185, 129, 0.1);
  padding: 0.25rem 0.5rem;
  border-radius: var(--radius-sm);
}

.root-card-origin {
  font-size: 0.75rem;
  color: var(--color-text-muted);
}

.root-card-title {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--color-text);
}

.root-card-meaning {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  line-height: 1.5;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* Learning Card */
.learn-card {
  max-width: 800px;
  margin: 2rem auto;
  background: var(--color-surface);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}

.learn-card-header {
  padding: 2rem;
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
}

.learn-card-header h2 {
  color: white;
  margin-bottom: 0.5rem;
}

.learn-card-header .meta {
  opacity: 0.9;
  font-size: 0.875rem;
}

.learn-card-body {
  padding: 2rem;
}

.learn-card-section {
  margin-bottom: 2rem;
}

.learn-card-section:last-child {
  margin-bottom: 0;
}

.learn-card-section h3 {
  font-size: 1.125rem;
  margin-bottom: 1rem;
  color: var(--color-primary);
}

.learn-card-section p {
  color: var(--color-text);
  line-height: 1.8;
}

/* Navigation Controls */
.nav-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.5rem 2rem;
  background: var(--color-background);
  border-top: 1px solid var(--color-border);
}

.nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.25rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.nav-btn:hover:not(:disabled) {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.nav-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.nav-progress {
  font-size: 0.875rem;
  color: var(--color-text-muted);
}

/* Footer */
.footer {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: 3rem 0;
  margin-top: 4rem;
}

.footer-content {
  text-align: center;
  max-width: 600px;
  margin: 0 auto;
}

.footer-tagline {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 1rem;
  color: var(--color-text);
}

.footer-description {
  color: var(--color-text-muted);
  font-size: 0.9375rem;
  line-height: 1.7;
}

.footer-links {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin-top: 1.5rem;
}

.footer-links a {
  color: var(--color-text-muted);
  font-size: 0.875rem;
}

.footer-links a:hover {
  color: var(--color-primary);
}

/* Page Header */
.page-header {
  text-align: center;
  padding: 3rem 0 2rem;
}

.page-header h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

.page-header p {
  color: var(--color-text-muted);
}

/* Example Cards */
.example-card {
  padding: 1.25rem;
  background: var(--color-background);
  border-radius: var(--radius-md);
  margin-bottom: 1rem;
}

.example-card:last-child {
  margin-bottom: 0;
}

.example-card h4 {
  font-size: 1rem;
  margin-bottom: 0.5rem;
  color: var(--color-text);
}

.example-card .label {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
}

.example-card p {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin: 0;
}

/* Progress Page Styles */
.progress-stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1.5rem;
  margin-bottom: 3rem;
}

.progress-stat-card {
  background: var(--color-surface);
  padding: 2rem;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  text-align: center;
}

.progress-stat-card h3 {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-bottom: 0.5rem;
  font-weight: 500;
}

.progress-stat-card .value {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--color-primary);
}

.mastery-list {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
}

.mastery-list-header {
  padding: 1.25rem 1.5rem;
  background: var(--color-background);
  border-bottom: 1px solid var(--color-border);
  font-weight: 600;
}

.mastery-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--color-border);
}

.mastery-item:last-child {
  border-bottom: none;
}

.mastery-item-info {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.mastery-item-id {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-primary);
  color: white;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  font-weight: 600;
}

.mastery-item-title {
  font-weight: 500;
}

/* Empty State */
.empty-state {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--color-text-muted);
}

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

.empty-state h3 {
  margin-bottom: 0.5rem;
  color: var(--color-text);
}

/* Responsive */
@media (max-width: 768px) {
  .hero {
    padding: 4rem 0 3rem;
  }
  
  .hero-title {
    font-size: 2rem;
  }
  
  .hero-subtitle {
    font-size: 1rem;
  }
  
  .hero-actions {
    flex-direction: column;
    align-items: center;
  }
  
  .nav-links {
    display: none;
  }
  
  .flashcard {
    height: 350px;
  }
  
  .flashcard-title {
    font-size: 1.5rem;
  }
  
  .learn-card-header,
  .learn-card-body {
    padding: 1.5rem;
  }
  
  .nav-controls {
    flex-direction: column;
    gap: 1rem;
  }
}

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

.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mt-4 { margin-top: 2rem; }

.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }
.mb-4 { margin-bottom: 2rem; }

.hidden { display: none; }

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

/* Selection */
::selection {
  background: rgba(16, 185, 129, 0.2);
  color: var(--color-text);
}