:root {
  --primary-color: #6b5ce7;
  --accent-color: #9c27b0;
  --text-primary: #1a1a2e;
  --text-secondary: #4a4a68;
  --text-muted: #6b6b8a;
  --bg-primary: #ffffff;
  --bg-secondary: #f8f9fc;
  --bg-tertiary: #f0f2f8;
  --border-color: #e2e5ef;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.1);
  --shadow-lg: 0 8px 24px rgba(0,0,0,0.12);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --max-width: 1200px;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.6;
  color: var(--text-primary);
  background: var(--bg-primary);
}

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

ul {
  list-style: none;
}

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

.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
}

.nav {
  display: flex;
  gap: 32px;
}

.nav a {
  color: var(--text-secondary);
  font-weight: 500;
  transition: color 0.2s;
}

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

.search-box {
  position: relative;
}

.search-box input {
  width: 240px;
  padding: 8px 16px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  background: var(--bg-secondary);
}

.search-box input::placeholder {
  color: var(--text-muted);
}

/* Main Content */
.main {
  min-height: calc(100vh - 64px - 200px);
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* Hero Section */
.hero {
  background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-tertiary) 100%);
  padding: 80px 0;
  text-align: center;
}

.hero-title {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 16px;
}

.hero-desc {
  font-size: 1.125rem;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto 40px;
}

.hero-search {
  max-width: 560px;
  margin: 0 auto 40px;
}

.hero-search input {
  width: 100%;
  padding: 16px 24px;
  border: 2px solid var(--border-color);
  border-radius: var(--radius-lg);
  font-size: 1rem;
  background: var(--bg-primary);
  box-shadow: var(--shadow-sm);
}

.quick-links {
  display: flex;
  justify-content: center;
  gap: 16px;
  flex-wrap: wrap;
}

.quick-link {
  padding: 12px 24px;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  font-weight: 500;
  transition: all 0.2s;
}

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

/* Section Title */
.section-title {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 24px;
}

/* Topics Section */
.topics-section {
  padding: 60px 0;
}

.topics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
}

.topic-card {
  padding: 24px;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  transition: all 0.2s;
}

.topic-card:hover {
  border-color: var(--primary-color);
  box-shadow: var(--shadow-md);
}

.topic-card h3 {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 8px;
}

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

/* Articles Section */
.articles-section {
  padding: 60px 0;
  background: var(--bg-secondary);
}

.articles-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 32px;
}

.articles-column h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 16px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.article-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.article-item {
  padding: 12px 16px;
  background: var(--bg-primary);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  transition: all 0.2s;
}

.article-item:hover {
  border-color: var(--primary-color);
}

.article-item a {
  color: var(--text-primary);
  font-size: 0.9375rem;
}

/* Breadcrumb */
.breadcrumb {
  padding: 20px 0;
  font-size: 0.875rem;
  color: var(--text-muted);
}

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

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

.breadcrumb span {
  margin: 0 8px;
}

/* Category Page */
.category-header {
  padding: 40px 0;
  border-bottom: 1px solid var(--border-color);
}

.category-header h1 {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 12px;
}

.category-header p {
  color: var(--text-secondary);
  max-width: 600px;
}

/* Modules Section */
.modules-section {
  padding: 40px 0;
}

.module-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.module-card {
  padding: 24px;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  transition: all 0.2s;
}

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

.module-card h3 {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 8px;
}

.module-card p {
  color: var(--text-secondary);
  font-size: 0.9375rem;
}

/* Article Page */
.article-layout {
  display: grid;
  grid-template-columns: 240px 1fr 240px;
  gap: 40px;
  padding: 40px 0;
}

.sidebar-left {
  position: sticky;
  top: 100px;
  height: fit-content;
}

.sidebar-left h2 {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 16px;
}

.sidebar-left p {
  font-size: 0.9375rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

.article-content {
  max-width: 100%;
}

.article-content h1 {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 24px;
  padding-bottom: 16px;
  border-bottom: 2px solid var(--border-color);
}

.article-content h2 {
  font-size: 1.5rem;
  font-weight: 600;
  margin: 40px 0 16px;
  color: var(--text-primary);
}

.article-content h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin: 32px 0 12px;
}

.article-content p {
  color: var(--text-secondary);
  margin-bottom: 16px;
  line-height: 1.8;
}

.article-content ul, .article-content ol {
  margin: 16px 0;
  padding-left: 24px;
}

.article-content li {
  color: var(--text-secondary);
  margin-bottom: 8px;
  line-height: 1.7;
}

.code-block {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 20px;
  margin: 20px 0;
  font-family: 'Monaco', 'Menlo', monospace;
  font-size: 0.875rem;
  overflow-x: auto;
}

.code-block .comment {
  color: var(--text-muted);
}

.toc {
  position: sticky;
  top: 100px;
  height: fit-content;
}

.toc h3 {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 16px;
}

.toc ul {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.toc a {
  color: var(--text-muted);
  font-size: 0.875rem;
  transition: color 0.2s;
}

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

/* Recommended Section */
.recommended-section {
  padding: 40px 0;
  border-top: 1px solid var(--border-color);
}

.recommended-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 32px;
}

.tag {
  padding: 8px 16px;
  background: var(--bg-secondary);
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  color: var(--text-secondary);
  transition: all 0.2s;
}

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

/* 404 Page */
.error-page {
  min-height: calc(100vh - 64px - 200px);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 80px 24px;
}

.error-code {
  font-size: 8rem;
  font-weight: 700;
  color: var(--primary-color);
  line-height: 1;
  margin-bottom: 24px;
}

.error-title {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 12px;
}

.error-desc {
  color: var(--text-secondary);
  margin-bottom: 32px;
}

.btn {
  display: inline-block;
  padding: 12px 32px;
  background: var(--primary-color);
  color: white;
  border-radius: var(--radius-md);
  font-weight: 500;
  transition: all 0.2s;
}

.btn:hover {
  background: var(--accent-color);
  box-shadow: var(--shadow-md);
}

/* Footer */
.footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  padding: 48px 0;
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.footer-brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--primary-color);
}

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

.footer-links {
  display: flex;
  gap: 24px;
}

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

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

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

  .article-layout {
    grid-template-columns: 1fr;
  }

  .sidebar-left, .toc {
    position: static;
    display: none;
  }
}

@media (max-width: 768px) {
  .header-inner {
    padding: 0 16px;
  }

  .nav {
    display: none;
  }

  .search-box {
    display: none;
  }

  .hero {
    padding: 60px 0;
  }

  .hero-title {
    font-size: 1.75rem;
  }

  .hero-desc {
    font-size: 1rem;
  }

  .articles-grid {
    grid-template-columns: 1fr;
  }

  .container {
    padding: 0 16px;
  }

  .footer-inner {
    flex-direction: column;
    gap: 24px;
    text-align: center;
  }

  .code-block {
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
}