/* ============================================================
   极客时间 — 共享样式系统
   CSS Tokens / Header / Footer / Components / Responsive
   ============================================================ */

/* ---------- CSS Custom Properties ---------- */
:root {
  --geek-green:       #00A870;
  --geek-green-hover: #00945E;
  --geek-green-light: #E6F7EF;
  --geek-green-pale:  #F0FBF5;

  --bg:               #F6F7FA;
  --surface:          #FFFFFF;
  --fg:               #1D2129;
  --fg-secondary:     #4E5969;
  --muted:            #86909C;
  --placeholder:      #C9CDD4;
  --border:           #E5E6EB;
  --border-light:     #F2F3F5;

  --accent:           #F53F3F;
  --accent-light:     #FFECE8;
  --gold:             #FF7D00;
  --gold-light:       #FFF7E8;

  --font-display:     -apple-system, BlinkMacSystemFont, 'PingFang SC', 'Microsoft YaHei', 'Helvetica Neue', sans-serif;
  --font-body:        -apple-system, BlinkMacSystemFont, 'PingFang SC', 'Microsoft YaHei', 'Helvetica Neue', sans-serif;
  --font-mono:        'SF Mono', 'JetBrains Mono', ui-monospace, 'Menlo', monospace;

  --radius-sm:        6px;
  --radius-md:        10px;
  --radius-lg:        16px;

  --shadow-sm:        0 1px 3px rgba(0,0,0,.06);
  --shadow-md:        0 4px 12px rgba(0,0,0,.08);
  --shadow-lg:        0 8px 24px rgba(0,0,0,.12);

  --header-height:    60px;

  --max-width:        1200px;
  --gutter:           24px;
}

/* ---------- Reset ---------- */
*, *::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-body);
  color: var(--fg);
  background: var(--bg);
  line-height: 1.6;
  min-height: 100vh;
  padding-top: var(--header-height);
}

a { color: inherit; text-decoration: none; }
ul, ol { list-style: none; }
img { max-width: 100%; display: block; }
button { font-family: inherit; cursor: pointer; border: none; background: none; }
input, select { font-family: inherit; }

/* ---------- Header ---------- */
.site-header {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--header-height);
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  z-index: 1000;
  display: flex;
  align-items: center;
}

.header-inner {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--gutter);
  display: flex;
  align-items: center;
  gap: 28px;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-shrink: 0;
  font-size: 20px;
  font-weight: 700;
  color: var(--fg);
}

.header-logo .logo-icon {
  width: 32px; height: 32px;
  background: var(--geek-green);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-size: 14px;
  font-weight: 900;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 4px;
  flex: 1;
}

.header-nav a {
  display: block;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  font-size: 14px;
  color: var(--fg-secondary);
  white-space: nowrap;
  transition: color .15s, background .15s;
}

.header-nav a:hover { color: var(--fg); background: var(--bg); }
.header-nav a.active { color: var(--geek-green); font-weight: 600; }

.header-search {
  position: relative;
  width: 240px;
  flex-shrink: 0;
}

.header-search input {
  width: 100%;
  height: 36px;
  padding: 0 40px 0 16px;
  border: 1px solid var(--border);
  border-radius: 20px;
  font-size: 13px;
  background: var(--bg);
  outline: none;
  transition: border-color .15s, background .15s;
}

.header-search input:focus {
  border-color: var(--geek-green);
  background: var(--surface);
}

.header-search .search-icon {
  position: absolute;
  right: 14px;
  top: 50%;
  transform: translateY(-50%);
  width: 16px; height: 16px;
  color: var(--muted);
  pointer-events: none;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-shrink: 0;
}

.header-actions .btn-outline {
  padding: 6px 18px;
  border: 1px solid var(--geek-green);
  color: var(--geek-green);
  border-radius: 20px;
  font-size: 13px;
  font-weight: 500;
  transition: all .15s;
}

.header-actions .btn-outline:hover {
  background: var(--geek-green);
  color: #fff;
}

.header-actions .btn-primary-sm {
  padding: 6px 18px;
  background: var(--geek-green);
  color: #fff;
  border-radius: 20px;
  font-size: 13px;
  font-weight: 500;
  transition: background .15s;
}

.header-actions .btn-primary-sm:hover { background: var(--geek-green-hover); }

.user-avatar {
  width: 36px; height: 36px;
  border-radius: 50%;
  background: var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  color: var(--muted);
}

/* ---------- Footer ---------- */
.site-footer {
  background: #1D2129;
  color: #C9CDD4;
  padding: 60px 0 0;
  margin-top: 80px;
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--gutter);
  display: grid;
  grid-template-columns: 1.5fr 1fr 1fr 1fr 1fr;
  gap: 40px;
}

.footer-brand .logo-text {
  font-size: 22px;
  font-weight: 700;
  color: #fff;
  margin-bottom: 12px;
}

.footer-brand p {
  font-size: 13px;
  line-height: 1.8;
  color: #86909C;
}

.footer-col h4 {
  font-size: 14px;
  font-weight: 600;
  color: #E5E6EB;
  margin-bottom: 16px;
}

.footer-col a {
  display: block;
  font-size: 13px;
  color: #86909C;
  padding: 4px 0;
  transition: color .15s;
}

.footer-col a:hover { color: #fff; }

.footer-bottom {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 24px var(--gutter);
  border-top: 1px solid rgba(255,255,255,.08);
  margin-top: 48px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 12px;
  color: #86909C;
}

.footer-bottom .links { display: flex; gap: 24px; }
.footer-bottom .links a { color: #86909C; }
.footer-bottom .links a:hover { color: #fff; }

/* ---------- Page Template ---------- */
.page-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--gutter);
}

.section-title {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  margin-bottom: 24px;
}

.section-title h2 {
  font-size: 22px;
  font-weight: 700;
  color: var(--fg);
}

.section-title .more {
  font-size: 14px;
  color: var(--muted);
  display: flex;
  align-items: center;
  gap: 4px;
  transition: color .15s;
}

.section-title .more:hover { color: var(--geek-green); }

.section-subtitle {
  font-size: 14px;
  color: var(--muted);
  margin-top: 4px;
}

/* ---------- Cards ---------- */
.card {
  background: var(--surface);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-light);
  overflow: hidden;
  transition: box-shadow .2s, transform .2s;
}

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

/* ---------- Course Card (通用) ---------- */
.course-card { cursor: pointer; }
.course-card .card-cover {
  aspect-ratio: 16 / 9;
  position: relative;
  overflow: hidden;
}

.course-card .card-cover::after {
  content: '';
  position: absolute;
  inset: 0;
  opacity: .15;
  background-image:
    radial-gradient(circle at 80% 20%, rgba(255,255,255,.6) 0%, transparent 50%),
    radial-gradient(circle at 20% 80%, rgba(255,255,255,.3) 0%, transparent 40%),
    radial-gradient(circle at 60% 60%, rgba(255,255,255,.2) 0%, transparent 30%);
}

.course-card .card-cover img {
  width: 100%; height: 100%;
  object-fit: cover;
}

.course-card .cover-tag {
  position: absolute;
  top: 10px; left: 10px;
  padding: 2px 8px;
  background: rgba(0,0,0,.45);
  color: #fff;
  font-size: 11px;
  border-radius: 3px;
}

.course-card .cover-promo {
  position: absolute;
  top: 10px; right: 10px;
  padding: 3px 10px;
  background: var(--accent);
  color: #fff;
  font-size: 11px;
  border-radius: 3px;
  font-weight: 500;
}

.course-card .card-cover-top {
  position: absolute;
  top: 0; left: 0; right: 0;
  bottom: 50%;
  display: flex;
  align-items: flex-end;
  padding: 16px;
  font-size: 40px;
  font-weight: 700;
  letter-spacing: -.02em;
  opacity: .15;
  color: currentColor;
}

.course-card .card-body { padding: 16px; }
.course-card .card-title {
  font-size: 15px;
  font-weight: 600;
  color: var(--fg);
  line-height: 1.4;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.course-card .card-meta {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-top: 10px;
  font-size: 12px;
  color: var(--muted);
}

.course-card .card-meta .difficulty {
  padding: 1px 6px;
  border-radius: 3px;
  font-size: 11px;
  background: var(--geek-green-light);
  color: var(--geek-green);
}

.course-card .card-author {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: 10px;
  font-size: 12px;
  color: var(--fg-secondary);
}

.course-card .card-author .author-avatar {
  width: 22px; height: 22px;
  border-radius: 50%;
  background: var(--border);
  flex-shrink: 0;
}

.course-card .card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  border-top: 1px solid var(--border-light);
  font-size: 12px;
  color: var(--muted);
}

.course-card .card-footer .price {
  font-size: 18px;
  font-weight: 700;
  color: var(--accent);
}

.course-card .card-footer .price small {
  font-size: 12px;
  font-weight: 400;
}

.course-card .card-footer .price .original {
  font-size: 13px;
  color: var(--muted);
  text-decoration: line-through;
  margin-left: 6px;
  font-weight: 400;
}

/* ---------- Tags / Pills ---------- */
.tag {
  display: inline-flex;
  align-items: center;
  padding: 3px 10px;
  border-radius: 4px;
  font-size: 12px;
  font-weight: 500;
  white-space: nowrap;
}

.tag-green { background: var(--geek-green-light); color: var(--geek-green); }
.tag-red { background: var(--accent-light); color: var(--accent); }
.tag-gold { background: var(--gold-light); color: var(--gold); }
.tag-gray { background: var(--bg); color: var(--fg-secondary); }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 24px;
  border-radius: var(--radius-sm);
  font-size: 14px;
  font-weight: 500;
  transition: all .15s;
}

.btn-primary {
  background: var(--geek-green);
  color: #fff;
}

.btn-primary:hover { background: var(--geek-green-hover); }

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

.btn-secondary:hover { border-color: var(--geek-green); color: var(--geek-green); }

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

.btn-accent:hover { opacity: .9; }

.btn-lg { padding: 12px 32px; font-size: 16px; border-radius: var(--radius-md); }
.btn-sm { padding: 6px 14px; font-size: 12px; }

/* ---------- Grid Helpers ---------- */
.course-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.course-grid-5 {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 16px;
}

.course-grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.course-grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}

/* ---------- Banner ---------- */
.hero-banner {
  position: relative;
  border-radius: var(--radius-lg);
  overflow: hidden;
  background: linear-gradient(135deg, #1a3a2a 0%, #0d2137 40%, #1a1a2e 100%);
  color: #fff;
  display: flex;
  min-height: 300px;
}

.hero-banner .banner-content {
  flex: 1;
  padding: 48px 40px;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.hero-banner .banner-tag {
  display: inline-block;
  padding: 4px 12px;
  background: rgba(255,255,255,.15);
  border-radius: 4px;
  font-size: 13px;
  margin-bottom: 16px;
  width: fit-content;
}

.hero-banner .banner-title {
  font-size: 32px;
  font-weight: 700;
  line-height: 1.3;
  margin-bottom: 12px;
}

.hero-banner .banner-desc {
  font-size: 15px;
  color: rgba(255,255,255,.7);
  line-height: 1.6;
  margin-bottom: 24px;
  max-width: 480px;
}

.hero-banner .banner-visual {
  width: 400px;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(255,255,255,.05);
}

/* ---------- Category Nav (首页分类入口) ---------- */
.category-nav {
  display: grid;
  grid-template-columns: repeat(7, 1fr);
  gap: 16px;
}

.category-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  padding: 20px 12px;
  background: var(--surface);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-light);
  cursor: pointer;
  transition: all .2s;
}

.category-item:hover {
  border-color: var(--geek-green);
  box-shadow: 0 2px 8px rgba(0,168,112,.1);
}

.category-item .cat-icon {
  width: 44px; height: 44px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 22px;
}

.cat-icon-text {
  font-size: 16px;
  font-weight: 700;
  line-height: 1;
}

.category-item .cat-name {
  font-size: 13px;
  font-weight: 500;
  color: var(--fg);
}

/* ---------- Promo Card ---------- */
.promo-card {
  display: flex;
  align-items: center;
  padding: 20px 24px;
  background: var(--surface);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-light);
  gap: 16px;
  cursor: pointer;
  transition: all .2s;
}

.promo-card:hover { box-shadow: var(--shadow-sm); }
.promo-card .promo-icon {
  width: 48px; height: 48px;
  border-radius: var(--radius-sm);
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
}

.promo-card .promo-info h4 {
  font-size: 14px;
  font-weight: 600;
  color: var(--fg);
}

.promo-card .promo-info p {
  font-size: 12px;
  color: var(--muted);
  margin-top: 2px;
}

/* ---------- Tabs / Filter Bar ---------- */
.filter-bar {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  padding: 16px 0;
}

.filter-pill {
  padding: 6px 16px;
  border-radius: 20px;
  font-size: 13px;
  color: var(--fg-secondary);
  background: var(--surface);
  border: 1px solid var(--border);
  cursor: pointer;
  transition: all .15s;
  white-space: nowrap;
}

.filter-pill:hover { border-color: var(--geek-green); color: var(--geek-green); }
.filter-pill.active {
  background: var(--geek-green);
  color: #fff;
  border-color: var(--geek-green);
}

/* ---------- Sidebar ---------- */
.sidebar-section {
  background: var(--surface);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-light);
  padding: 20px;
  margin-bottom: 16px;
}

.sidebar-section h3 {
  font-size: 15px;
  font-weight: 600;
  color: var(--fg);
  margin-bottom: 14px;
}

/* ---------- Spacing ---------- */
.section { padding: 48px 0; }
.section-sm { padding: 32px 0; }
.section-lg { padding: 64px 0; }

.mt-16 { margin-top: 16px; }
.mt-24 { margin-top: 24px; }
.mt-32 { margin-top: 32px; }
.mb-16 { margin-bottom: 16px; }
.mb-24 { margin-bottom: 24px; }
.mb-32 { margin-bottom: 32px; }

/* ---------- Responsive ---------- */
@media (max-width: 1280px) {
  .course-grid { grid-template-columns: repeat(3, 1fr); }
  .course-grid-5 { grid-template-columns: repeat(4, 1fr); }
  .category-nav { grid-template-columns: repeat(4, 1fr); }
}

@media (max-width: 1024px) {
  .course-grid { grid-template-columns: repeat(2, 1fr); }
  .course-grid-5, .course-grid-3 { grid-template-columns: repeat(2, 1fr); }
  .category-nav { grid-template-columns: repeat(3, 1fr); }
  .hero-banner { flex-direction: column; }
  .hero-banner .banner-visual { width: 100%; height: 200px; }
  .footer-inner { grid-template-columns: 1fr 1fr 1fr; }
}

@media (max-width: 768px) {
  :root { --gutter: 16px; }
  .header-nav { display: none; }
  .header-search { width: 160px; }
  .course-grid, .course-grid-5, .course-grid-3, .course-grid-2 { grid-template-columns: repeat(2, 1fr); gap: 12px; }
  .category-nav { grid-template-columns: repeat(2, 1fr); }
  .hero-banner .banner-content { padding: 32px 24px; }
  .hero-banner .banner-title { font-size: 24px; }
  .footer-inner { grid-template-columns: 1fr 1fr; }
  .section { padding: 32px 0; }
}

@media (max-width: 480px) {
  .course-grid, .course-grid-5, .course-grid-3, .course-grid-2 { grid-template-columns: 1fr; }
  .category-nav { grid-template-columns: repeat(2, 1fr); }
  .footer-inner { grid-template-columns: 1fr; }
  .hero-banner { min-height: 240px; }
  .hero-banner .banner-content { padding: 24px 16px; }
  .hero-banner .banner-title { font-size: 20px; }
}