/* ===========================
   CSS Variables & Theming
   =========================== */

:root {
  --color-primary: #4f46e5;
  --color-primary-dark: #3730a3;
  --color-primary-light: #eef2ff;
  --color-primary-hover: #4338ca;
  --color-accent: #06b6d4;
  --color-accent-light: #ecfeff;
  --color-bg: #f8fafc;
  --color-surface: #ffffff;
  --color-surface-alt: #f1f5f9;
  --color-surface-translucent: rgba(255, 255, 255, 0.85);
  --color-border: #e2e8f0;
  --color-border-hover: #cbd5e1;
  --color-text: #0f172a;
  --color-text-secondary: #475569;
  --color-text-muted: #94a3b8;
  --shadow-sm: 0 1px 2px 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);
  --container-max: 1200px;
  --header-height: 60px;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI',
    'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'JetBrains Mono', monospace;
  --transition-fast: 150ms ease;
  --transition-base: 200ms ease;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-primary: #818cf8;
    --color-primary-dark: #6366f1;
    --color-primary-light: rgba(99, 102, 241, 0.15);
    --color-primary-hover: #a5b4fc;
    --color-accent: #22d3ee;
    --color-accent-light: rgba(34, 211, 238, 0.1);
    --color-bg: #0f172a;
    --color-surface: #1e293b;
    --color-surface-alt: #162033;
    --color-surface-translucent: rgba(30, 41, 59, 0.9);
    --color-border: #334155;
    --color-border-hover: #475569;
    --color-text: #f1f5f9;
    --color-text-secondary: #94a3b8;
    --color-text-muted: #64748b;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
  }
}

/* ===========================
   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;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

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

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

/* ===========================
   Layout
   =========================== */

.container {
  width: 100%;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.main-content { flex: 1; }

/* ===========================
   Typography
   =========================== */

h1, h2, h3, h4, h5, h6 { font-weight: 700; line-height: 1.3; color: var(--color-text); }
h1 { font-size: 2rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.25rem; }
h4 { font-size: 1.125rem; }
p { line-height: 1.7; }

/* ===========================
   Buttons
   =========================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.625rem 1.5rem;
  font-size: 0.9375rem;
  font-weight: 600;
  font-family: var(--font-sans);
  border-radius: 0.5rem;
  border: 1px solid transparent;
  cursor: pointer;
  transition: all var(--transition-base);
  text-decoration: none;
  gap: 0.5rem;
  line-height: 1.4;
}
.btn:disabled { opacity: 0.6; cursor: not-allowed; }
.btn-primary { background: var(--color-primary); color: #fff; border-color: var(--color-primary); }
.btn-primary:hover:not(:disabled) { background: var(--color-primary-hover); border-color: var(--color-primary-hover); }
.btn-outline { background: transparent; color: var(--color-primary); border-color: var(--color-primary); }
.btn-outline:hover:not(:disabled) { background: var(--color-primary); color: #fff; }

/* ===========================
   Header
   =========================== */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  border-bottom: 1px solid var(--color-border);
  backdrop-filter: blur(12px);
  background: var(--color-surface-translucent);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 60px;
}

.header-brand {
  display: flex;
  align-items: center;
  gap: 0.625rem;
  text-decoration: none;
  color: var(--color-primary);
}

.brand-icon { flex-shrink: 0; }

.brand-text {
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--color-text);
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.nav-link {
  padding: 0.5rem 1rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: 0.9375rem;
  font-weight: 500;
  border-radius: 0.5rem;
  transition: all 0.2s;
  background: none;
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}
.nav-link:hover, .nav-link.active { color: var(--color-primary); background: var(--color-primary-light); }

.nav-dropdown { position: relative; }

.dropdown-menu {
  position: absolute;
  top: calc(100% + 0.5rem);
  right: 0;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 0.75rem;
  padding: 0.5rem;
  min-width: 200px;
  box-shadow: 0 8px 30px rgba(0, 0, 0, 0.12);
  display: none;
}
.nav-dropdown:hover .dropdown-menu { display: block; }

.dropdown-item {
  display: block;
  padding: 0.625rem 1rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: 0.9375rem;
  border-radius: 0.5rem;
  transition: all 0.15s;
}
.dropdown-item:hover { background: var(--color-primary-light); color: var(--color-primary); }

.dropdown-arrow { transition: transform 0.2s; }
.nav-dropdown:hover .dropdown-arrow { transform: rotate(180deg); }

/* Mobile */
.mobile-toggle { display: none; }

@media (max-width: 768px) {
  .header-nav { display: none; }
  .mobile-toggle {
    display: block;
    background: none;
    border: none;
    color: var(--color-text);
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 0.5rem;
  }
}

/* ===========================
   Footer
   =========================== */

.site-footer {
  background: var(--color-surface-alt);
  border-top: 1px solid var(--color-border);
  padding: 3rem 0 1.5rem;
  margin-top: auto;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 2rem;
  margin-bottom: 2.5rem;
}

.footer-brand {
  display: inline-block;
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--color-text);
  text-decoration: none;
  margin-bottom: 0.75rem;
}

.footer-description {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
  max-width: 360px;
}

.footer-heading {
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: 1rem;
  letter-spacing: 0.02em;
}

.footer-links { display: flex; flex-direction: column; gap: 0.5rem; }
.footer-links a {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  transition: color 0.15s;
}
.footer-links a:hover { color: var(--color-primary); }

.footer-bottom {
  border-top: 1px solid var(--color-border);
  padding-top: 1.5rem;
  text-align: center;
}

.copyright { font-size: 0.8125rem; color: var(--color-text-muted); }

@media (max-width: 768px) {
  .footer-grid { grid-template-columns: 1fr 1fr; gap: 2rem 1.5rem; }
  .footer-brand-section { grid-column: 1 / -1; }
}
@media (max-width: 480px) {
  .footer-grid { grid-template-columns: 1fr; }
}

/* ===========================
   Hero
   =========================== */

.hero {
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
  color: #fff;
  padding: 4rem 0 3rem;
  text-align: center;
}

.hero-title {
  font-size: 2.5rem;
  font-weight: 800;
  margin-bottom: 1rem;
  letter-spacing: -0.02em;
  color: #fff;
}

.hero-description {
  font-size: 1.125rem;
  opacity: 0.9;
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.7;
}

/* ===========================
   Category Filter
   =========================== */

.category-filter {
  padding: 1.5rem 0;
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 60px;
  z-index: 40;
}

.filter-tabs {
  display: flex;
  gap: 0.5rem;
  overflow-x: auto;
  padding-bottom: 0.25rem;
  -webkit-overflow-scrolling: touch;
}

.filter-tab {
  padding: 0.5rem 1.25rem;
  border: 1px solid var(--color-border);
  border-radius: 2rem;
  background: transparent;
  color: var(--color-text-secondary);
  font-size: 0.875rem;
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.2s ease;
  text-decoration: none;
}
.filter-tab:hover { border-color: var(--color-primary); color: var(--color-primary); }
.filter-tab.active { background: var(--color-primary); border-color: var(--color-primary); color: #fff; }

/* ===========================
   Article Grid
   =========================== */

.article-list-section { padding: 2rem 0 4rem; }

.article-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: 1.5rem;
}

/* ===========================
   Article Card
   =========================== */

.article-card {
  display: flex;
  flex-direction: column;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 0.75rem;
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  transition: all 0.25s ease;
}
.article-card:hover {
  border-color: var(--color-primary);
  box-shadow: 0 4px 20px rgba(79, 70, 229, 0.1);
  transform: translateY(-2px);
}

.card-image {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  background: var(--color-surface-alt);
}
.card-image img { width: 100%; height: 100%; object-fit: cover; transition: transform 0.3s ease; }
.article-card:hover .card-image img { transform: scale(1.03); }

.card-image-placeholder {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  background: linear-gradient(135deg, var(--color-surface-alt) 0%, var(--color-border) 100%);
  min-height: 180px;
}

.card-body { flex: 1; display: flex; flex-direction: column; padding: 1.25rem; }

.card-meta { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; }

.card-category {
  display: inline-block;
  padding: 0.15rem 0.5rem;
  background: var(--color-primary-light);
  color: var(--color-primary);
  border-radius: 0.25rem;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.02em;
}

.card-date { font-size: 0.8125rem; color: var(--color-text-muted); }

.card-title {
  font-size: 1.0625rem;
  font-weight: 700;
  line-height: 1.45;
  color: var(--color-text);
  margin-bottom: 0.5rem;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.card-summary {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: 1rem;
  flex: 1;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.card-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 0.75rem;
  border-top: 1px solid var(--color-border);
}

.card-source { font-size: 0.8125rem; color: var(--color-text-muted); }
.card-read-more { font-size: 0.8125rem; color: var(--color-primary); font-weight: 500; }

/* ===========================
   Article Detail
   =========================== */

.article-page { padding: 2rem 0 4rem; }

.breadcrumb {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-bottom: 2rem;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.4rem;
}
.breadcrumb a { color: var(--color-primary); text-decoration: none; }
.breadcrumb a:hover { text-decoration: underline; }
.breadcrumb .separator { color: var(--color-border); }
.breadcrumb .current {
  color: var(--color-text-secondary);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  max-width: 300px;
}

.article-header { margin-bottom: 2rem; }

.article-meta-top {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1rem;
  flex-wrap: wrap;
}

.category-badge {
  display: inline-block;
  padding: 0.25rem 0.75rem;
  background: var(--color-primary-light);
  color: var(--color-primary);
  border-radius: 2rem;
  font-size: 0.8125rem;
  font-weight: 600;
  text-decoration: none;
  transition: background 0.2s;
}
.category-badge:hover { background: var(--color-primary); color: #fff; }

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

.source-tag {
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  background: var(--color-surface-alt);
  padding: 0.2rem 0.6rem;
  border-radius: 0.25rem;
}

.article-title {
  font-size: 2rem;
  font-weight: 800;
  line-height: 1.3;
  color: var(--color-text);
  margin-bottom: 1rem;
  letter-spacing: -0.01em;
}

.article-summary {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
  border-left: 3px solid var(--color-primary);
  padding-left: 1rem;
}

.article-cover { margin-bottom: 2rem; border-radius: 0.75rem; overflow: hidden; }
.article-cover img { width: 100%; height: auto; display: block; }

/* Prose / Content */
.article-content {
  font-size: 1.0625rem;
  line-height: 1.8;
  color: var(--color-text);
  max-width: 780px;
}
.article-content h2 { font-size: 1.5rem; font-weight: 700; margin-top: 2.5rem; margin-bottom: 1rem; }
.article-content h3 { font-size: 1.25rem; font-weight: 600; margin-top: 2rem; margin-bottom: 0.75rem; }
.article-content p { margin-bottom: 1.25rem; }
.article-content img { max-width: 100%; height: auto; border-radius: 0.5rem; margin: 1.5rem 0; }
.article-content a { color: var(--color-primary); text-decoration: underline; text-underline-offset: 2px; }
.article-content blockquote {
  border-left: 3px solid var(--color-primary);
  padding-left: 1rem;
  margin: 1.5rem 0;
  color: var(--color-text-secondary);
  font-style: italic;
}
.article-content pre {
  background: var(--color-surface-alt);
  padding: 1rem 1.25rem;
  border-radius: 0.5rem;
  overflow-x: auto;
  margin: 1.5rem 0;
  font-family: var(--font-mono);
  font-size: 0.875rem;
  line-height: 1.6;
}
.article-content code { font-family: var(--font-mono); font-size: 0.875em; }
.article-content ul, .article-content ol { padding-left: 1.5rem; margin-bottom: 1.25rem; }
.article-content li { margin-bottom: 0.5rem; }
.article-content table { width: 100%; border-collapse: collapse; margin: 1.5rem 0; }
.article-content th, .article-content td { padding: 0.75rem 1rem; border: 1px solid var(--color-border); text-align: left; }
.article-content th { background: var(--color-surface-alt); font-weight: 600; }

/* FAQ Section */
.faq-section { margin-top: 3rem; padding-top: 2rem; border-top: 1px solid var(--color-border); }
.faq-title { font-size: 1.5rem; font-weight: 700; margin-bottom: 1.5rem; }
.faq-item { border: 1px solid var(--color-border); border-radius: 0.5rem; margin-bottom: 0.75rem; overflow: hidden; }
.faq-question {
  padding: 1rem 1.25rem;
  cursor: pointer;
  font-weight: 600;
  color: var(--color-text);
  background: var(--color-surface-alt);
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.faq-question::after { content: '+'; font-size: 1.25rem; color: var(--color-primary); flex-shrink: 0; margin-left: 1rem; }
details[open] .faq-question::after { content: '-'; }
.faq-question::-webkit-details-marker { display: none; }
.faq-answer { padding: 1rem 1.25rem; color: var(--color-text-secondary); line-height: 1.7; }

/* Article Footer */
.article-footer {
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--color-border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

.article-tags { display: flex; align-items: center; gap: 0.5rem; }
.tag-label { font-size: 0.875rem; color: var(--color-text-muted); }
.tag {
  display: inline-block;
  padding: 0.2rem 0.6rem;
  background: var(--color-surface-alt);
  color: var(--color-text-secondary);
  border-radius: 0.25rem;
  font-size: 0.8125rem;
  text-decoration: none;
  transition: all 0.2s;
}
.tag:hover { background: var(--color-primary-light); color: var(--color-primary); }
.original-link a { color: var(--color-primary); font-size: 0.9375rem; text-decoration: none; font-weight: 500; }
.original-link a:hover { text-decoration: underline; }

/* ===========================
   Topic Page
   =========================== */

.topic-hero {
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
  color: #fff;
  padding: 3rem 0 2.5rem;
}
.topic-hero .breadcrumb { opacity: 0.85; }
.topic-hero .breadcrumb a { color: #fff; opacity: 0.8; }
.topic-hero .breadcrumb a:hover { opacity: 1; }
.topic-hero .breadcrumb .separator { opacity: 0.5; }
.topic-title { font-size: 2rem; font-weight: 800; margin-bottom: 0.75rem; color: #fff; }
.topic-description { font-size: 1.0625rem; opacity: 0.9; max-width: 600px; line-height: 1.7; }

/* ===========================
   Empty States
   =========================== */

.empty-state { text-align: center; padding: 4rem 1rem; color: var(--color-text-secondary); }

/* ===========================
   Scrollbar
   =========================== */

::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--color-border); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--color-text-muted); }

::selection { background: var(--color-primary-light); color: var(--color-primary-dark); }

/* ===========================
   Responsive
   =========================== */

@media (max-width: 1024px) {
  .container { padding: 0 1.25rem; }
}

@media (max-width: 768px) {
  html { font-size: 15px; }
  .container { padding: 0 1rem; }
  .hero { padding: 3rem 0 2rem; }
  .hero-title { font-size: 1.75rem; }
  .hero-description { font-size: 1rem; }
  .article-grid { grid-template-columns: 1fr; }
  .article-title { font-size: 1.5rem; }
  .article-content { font-size: 1rem; }
  .topic-title { font-size: 1.5rem; }
}

@media (max-width: 480px) {
  html { font-size: 14px; }
}