/* CSS Variables for极简白净风 */
:root {
  --primary-color: #0066cc;
  --primary-dark: #004499;
  --primary-light: #e6f2ff;
  --background-color: #ffffff;
  --text-color: #333333;
  --text-light: #666666;
  --border-color: #e0e0e0;
  --card-background: #f8f9fa;
  --hover-color: #f5f5f5;
  --success-color: #28a745;
  --warning-color: #ffc107;
  --danger-color: #dc3545;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 20px rgba(0, 0, 0, 0.1);
  --border-radius: 8px;
  --transition: all 0.3s ease;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  line-height: 1.8;
  color: var(--text-color);
  background-color: var(--background-color);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.4;
  margin-bottom: 1rem;
  color: var(--text-color);
}

h1 {
  font-size: 2.5rem;
  margin-bottom: 1.5rem;
}

h2 {
  font-size: 2rem;
  margin-bottom: 1.25rem;
}

h3 {
  font-size: 1.5rem;
  margin-bottom: 1rem;
}

h4 {
  font-size: 1.25rem;
  margin-bottom: 0.75rem;
}

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

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

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

/* Layout */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

.header {
  background-color: var(--background-color);
  border-bottom: 1px solid var(--border-color);
  padding: 1rem 0;
  position: sticky;
  top: 0;
  z-index: 1000;
  box-shadow: var(--shadow-sm);
}

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

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
  text-decoration: none;
}

.logo:hover {
  text-decoration: none;
  color: var(--primary-dark);
}

.nav {
  display: flex;
  gap: 2rem;
  align-items: center;
}

.nav a {
  color: var(--text-color);
  font-weight: 500;
}

.nav a:hover {
  color: var(--primary-color);
  text-decoration: none;
}

.nav a.active {
  color: var(--primary-color);
  border-bottom: 2px solid var(--primary-color);
  padding-bottom: 0.25rem;
}

/* Search Box */
.search-box {
  position: relative;
}

.search-input {
  padding: 0.5rem 1rem;
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  font-size: 0.9rem;
  width: 250px;
  transition: var(--transition);
}

.search-input:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px var(--primary-light);
}

.search-btn {
  position: absolute;
  right: 0.5rem;
  top: 50%;
  transform: translateY(-50%);
  background: none;
  border: none;
  color: var(--text-light);
  cursor: pointer;
}

/* Main Content */
.main {
  padding: 2rem 0;
  min-height: calc(100vh - 200px);
}

/* Breadcrumb Navigation */
.breadcrumb {
  margin-bottom: 2rem;
  font-size: 0.9rem;
  color: var(--text-light);
}

.breadcrumb a {
  color: var(--text-light);
}

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

.breadcrumb span {
  margin: 0 0.5rem;
}

.breadcrumb .current {
  color: var(--text-color);
  font-weight: 500;
}

/* Hero Section */
.hero {
  background: linear-gradient(135deg, var(--primary-light) 0%, var(--background-color) 100%);
  padding: 3rem;
  border-radius: var(--border-radius);
  margin-bottom: 2rem;
  text-align: center;
}

.hero h1 {
  margin-bottom: 1rem;
}

.hero .subtitle {
  font-size: 1.2rem;
  color: var(--text-light);
  margin-bottom: 1.5rem;
}

.hero .description {
  max-width: 800px;
  margin: 0 auto;
  color: var(--text-color);
}

/* Cards */
.card {
  background-color: var(--card-background);
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  padding: 1.5rem;
  margin-bottom: 1rem;
  transition: var(--transition);
}

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

.card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

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

.card-title a {
  color: inherit;
  text-decoration: none;
}

.card-title a:hover {
  color: var(--primary-color);
}

.card-number {
  font-size: 0.9rem;
  color: var(--primary-color);
  font-weight: 600;
  background-color: var(--primary-light);
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
}

.card-content {
  color: var(--text-color);
  line-height: 1.6;
}

.card-meta {
  display: flex;
  gap: 1rem;
  margin-top: 1rem;
  font-size: 0.85rem;
  color: var(--text-light);
}

/* Knowledge Point Content */
.knowledge-content {
  max-width: 900px;
  margin: 0 auto;
}

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

.knowledge-section h3 {
  color: var(--primary-color);
  border-bottom: 2px solid var(--primary-light);
  padding-bottom: 0.5rem;
  margin-bottom: 1rem;
}

.knowledge-definition {
  background-color: var(--primary-light);
  padding: 1.5rem;
  border-radius: var(--border-radius);
  border-left: 4px solid var(--primary-color);
  margin-bottom: 1.5rem;
}

.knowledge-example {
  background-color: var(--card-background);
  padding: 1.5rem;
  border-radius: var(--border-radius);
  border-left: 4px solid var(--success-color);
  margin-bottom: 1.5rem;
}

.knowledge-formula {
  background-color: var(--card-background);
  padding: 1.5rem;
  border-radius: var(--border-radius);
  border-left: 4px solid var(--warning-color);
  margin-bottom: 1.5rem;
  font-family: 'Courier New', monospace;
  font-size: 1.1rem;
  text-align: center;
}

.knowledge-implication {
  background-color: var(--card-background);
  padding: 1.5rem;
  border-radius: var(--border-radius);
  border-left: 4px solid var(--danger-color);
  margin-bottom: 1.5rem;
}

.knowledge-extension {
  background-color: var(--card-background);
  padding: 1.5rem;
  border-radius: var(--border-radius);
  border-left: 4px solid var(--text-light);
  margin-bottom: 1.5rem;
}

/* Related Knowledge */
.related-knowledge {
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border-color);
}

.related-knowledge h3 {
  margin-bottom: 1.5rem;
}

.related-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 1rem;
}

.related-item {
  background-color: var(--card-background);
  padding: 1rem;
  border-radius: var(--border-radius);
  border: 1px solid var(--border-color);
  transition: var(--transition);
}

.related-item:hover {
  border-color: var(--primary-color);
  box-shadow: var(--shadow-sm);
}

.related-item a {
  color: var(--text-color);
  text-decoration: none;
  display: block;
}

.related-item a:hover {
  color: var(--primary-color);
}

.related-item .number {
  font-size: 0.85rem;
  color: var(--primary-color);
  font-weight: 600;
}

/* Footer */
.footer {
  background-color: var(--card-background);
  border-top: 1px solid var(--border-color);
  padding: 2rem 0;
  margin-top: 3rem;
}

.footer .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

.footer-content {
  max-width: 600px;
}

.footer-title {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
}

.footer-description {
  color: var(--text-light);
  font-size: 0.9rem;
}

.footer-links {
  display: flex;
  gap: 2rem;
}

.footer-links a {
  color: var(--text-light);
  font-size: 0.9rem;
}

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

.footer-copyright {
  width: 100%;
  text-align: center;
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border-color);
  color: var(--text-light);
  font-size: 0.85rem;
}

/* Language Switcher */
.lang-switch {
  display: flex;
  gap: 0.5rem;
  align-items: center;
}

.lang-btn {
  padding: 0.5rem 1rem;
  border: 1px solid var(--border-color);
  background-color: var(--background-color);
  color: var(--text-color);
  border-radius: var(--border-radius);
  cursor: pointer;
  transition: var(--transition);
}

.lang-btn:hover {
  border-color: var(--primary-color);
  color: var(--primary-color);
}

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

/* Language Selection Page */
.lang-selection {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: linear-gradient(135deg, var(--primary-light) 0%, var(--background-color) 100%);
}

.lang-card {
  background-color: var(--background-color);
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  padding: 3rem;
  text-align: center;
  box-shadow: var(--shadow-lg);
  max-width: 400px;
  width: 100%;
}

.lang-card h1 {
  margin-bottom: 1rem;
}

.lang-card p {
  color: var(--text-light);
  margin-bottom: 2rem;
}

.lang-options {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.lang-option {
  display: block;
  padding: 1.5rem;
  border: 2px solid var(--border-color);
  border-radius: var(--border-radius);
  text-decoration: none;
  color: var(--text-color);
  transition: var(--transition);
}

.lang-option:hover {
  border-color: var(--primary-color);
  background-color: var(--primary-light);
  text-decoration: none;
}

.lang-option h3 {
  margin-bottom: 0.5rem;
  color: var(--primary-color);
}

.lang-option p {
  margin-bottom: 0;
  font-size: 0.9rem;
}

/* Responsive Design */
@media (max-width: 768px) {
  .header .container {
    flex-direction: column;
    gap: 1rem;
  }
  
  .nav {
    flex-wrap: wrap;
    justify-content: center;
  }
  
  .search-input {
    width: 200px;
  }
  
  h1 {
    font-size: 2rem;
  }
  
  h2 {
    font-size: 1.5rem;
  }
  
  .hero {
    padding: 2rem;
  }
  
  .hero h1 {
    font-size: 1.8rem;
  }
  
  .card {
    padding: 1rem;
  }
  
  .footer .container {
    flex-direction: column;
    text-align: center;
  }
  
  .footer-links {
    flex-wrap: wrap;
    justify-content: center;
  }
  
  .related-list {
    grid-template-columns: 1fr;
  }
}

/* Print Styles */
@media print {
  .header, .footer, .search-box, .lang-switch {
    display: none;
  }
  
  .main {
    padding: 0;
  }
  
  .card {
    break-inside: avoid;
    box-shadow: none;
    border: 1px solid #ddd;
  }
}

/* Dark Mode Support */
@media (prefers-color-scheme: dark) {
  :root {
    --background-color: #1a1a1a;
    --text-color: #ffffff;
    --text-light: #b0b0b0;
    --border-color: #404040;
    --card-background: #2d2d2d;
    --hover-color: #333333;
    --primary-light: #1a3a5c;
  }
  
  body {
    background-color: var(--background-color);
    color: var(--text-color);
  }
  
  .header {
    background-color: var(--card-background);
  }
  
  .card {
    background-color: var(--card-background);
  }
  
  .knowledge-definition,
  .knowledge-example,
  .knowledge-formula,
  .knowledge-implication,
  .knowledge-extension {
    background-color: var(--card-background);
  }
}