:root {
  --bg: #f4f6fb;
  --card: #ffffff;
  --ink: #1f2430;
  --muted: #6b7280;
  --line: #e8ebf1;
  --shadow-sm: 0 1px 2px rgba(20, 30, 60, .05);
  --shadow-md: 0 8px 24px rgba(20, 30, 60, .10);
  --shadow-lg: 0 18px 44px rgba(20, 30, 60, .16);
  --blue: #2563eb;
  --violet: #7c3aed;
  --green: #059669;
  --amber: #d97706;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;
  line-height: 1.6;
  font-size: 15px;
  height: 100%;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
html { scroll-behavior: smooth; }
::selection {
  background: rgba(37, 99, 235, .2);
  color: inherit;
}
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb {
  background: rgba(107, 114, 128, .4);
  border-radius: 999px;
  border: 2px solid transparent;
  background-clip: padding-box;
}
::-webkit-scrollbar-thumb:hover { background-color: rgba(37, 99, 235, .55); }
html[data-theme="dark"] ::-webkit-scrollbar-thumb { background-color: rgba(139, 152, 173, .45); }

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

/* ===== 顶部导航 ===== */
.topbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, .86);
  backdrop-filter: saturate(160%) blur(10px);
  -webkit-backdrop-filter: saturate(160%) blur(10px);
  border-bottom: 1px solid var(--line);
  box-shadow: var(--shadow-sm);
}
.topbar-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 9px 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  flex-wrap: wrap;
}
.brand {
  font-weight: 800;
  font-size: 17px;
  color: var(--ink);
  white-space: nowrap;
  background: linear-gradient(120deg, #2563eb, #7c3aed, #059669);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}
.brand.active { color: var(--ink); }
.main-nav { display: flex; flex-wrap: wrap; gap: 4px; }
.main-nav a {
  padding: 6px 12px;
  border-radius: 999px;
  color: var(--muted);
  font-size: 13px;
  font-weight: 600;
  white-space: nowrap;
  transition: all .18s ease;
  position: relative;
}
.main-nav a::after {
  content: "";
  position: absolute;
  left: 50%;
  bottom: 1px;
  width: 0;
  height: 2px;
  border-radius: 999px;
  background: currentColor;
  opacity: .85;
  transform: translateX(-50%);
  transition: width .22s ease;
}
.main-nav a:hover::after { width: 60%; }
.main-nav a.active::after { width: 70%; background: #fff; }
.main-nav a:hover { background: #f1f5f9; color: var(--ink); transform: translateY(-1px); }
.main-nav a.active { color: #fff; box-shadow: 0 4px 12px rgba(20, 30, 60, .22); }
.main-nav a.c-blue.active { background: linear-gradient(120deg, #2563eb, #3b82f6); }
.main-nav a.c-violet.active { background: linear-gradient(120deg, #7c3aed, #8b5cf6); }
.main-nav a.c-green.active { background: linear-gradient(120deg, #059669, #10b981); }
.main-nav a.c-amber.active { background: linear-gradient(120deg, #d97706, #f59e0b); }

/* ===== Hero ===== */
.home-wrap { min-height: calc(100vh - 52px); }
.hero {
  position: relative;
  overflow: hidden;
  padding: 54px 16px 46px;
  text-align: center;
  background: linear-gradient(150deg, #1e3a8a 0%, #312e81 40%, #4c1d95 100%);
  color: #fff;
}
.hero::before {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background-image:
    linear-gradient(rgba(255, 255, 255, .05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, .05) 1px, transparent 1px);
  background-size: 40px 40px;
  mask-image: radial-gradient(ellipse 90% 80% at 50% 0%, rgba(0, 0, 0, .9), transparent 75%);
  -webkit-mask-image: radial-gradient(ellipse 90% 80% at 50% 0%, rgba(0, 0, 0, .9), transparent 75%);
}
.hero::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background: radial-gradient(900px 340px at 85% -60px, rgba(96, 165, 250, .35), transparent 60%);
}
.hero-inner { position: relative; z-index: 2; max-width: 780px; margin: 0 auto; }
.hero-kicker {
  font-size: 11px;
  letter-spacing: 3px;
  font-weight: 700;
  opacity: .72;
  margin: 0 0 12px;
}
.hero h1 {
  font-size: 34px;
  margin: 0 0 12px;
  letter-spacing: 2px;
  background: linear-gradient(120deg, #fff, #c7d2fe);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  text-wrap: balance;
}
.hero-sub {
  margin: 0 auto;
  max-width: 620px;
  font-size: 14px;
  line-height: 1.8;
  opacity: .85;
}

.blob {
  position: absolute;
  border-radius: 50%;
  filter: blur(60px);
  opacity: .38;
  z-index: 1;
  animation: blobFloat 14s ease-in-out infinite;
}
.blob-a { width: 340px; height: 340px; background: #2563eb; top: -140px; right: -80px; }
.blob-b { width: 300px; height: 300px; background: #7c3aed; bottom: -150px; left: -70px; animation-delay: -4s; }
.blob-c { width: 220px; height: 220px; background: #0d9488; top: 30px; left: 16%; opacity: .28; animation-delay: -8s; }
@keyframes blobFloat {
  0%, 100% { transform: translate(0, 0) scale(1); }
  33% { transform: translate(18px, -14px) scale(1.08); }
  66% { transform: translate(-14px, 12px) scale(.94); }
}

/* ===== 概览容器 ===== */
.container {
  max-width: 1080px;
  margin: 0 auto;
  padding: 28px 16px 44px;
}

.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(248px, 1fr));
  gap: 18px;
}

.course-card {
  position: relative;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 20px;
  cursor: pointer;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  gap: 12px;
  box-shadow: var(--shadow-sm);
  transition: transform .18s ease, box-shadow .18s ease;
}
.course-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  border-radius: 18px 18px 0 0;
  background: var(--theme);
}
.course-card::after {
  content: "";
  position: absolute;
  top: 0; bottom: 0;
  left: -80%;
  width: 55%;
  pointer-events: none;
  background: linear-gradient(105deg, transparent, rgba(255, 255, 255, .5), transparent);
  transform: skewX(-18deg);
  transition: left .55s ease;
}
.course-card:hover::after { left: 135%; }
html[data-theme="dark"] .course-card::after { background: linear-gradient(105deg, transparent, rgba(255, 255, 255, .07), transparent); }
.course-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-md); }
.course-card .c-icon { transition: transform .22s ease; }
.course-card:hover .c-icon { transform: scale(1.08) rotate(-4deg); }

.course-card.c-blue    { --theme: var(--blue); }
.course-card.c-violet  { --theme: var(--violet); }
.course-card.c-green   { --theme: var(--green); }
.course-card.c-amber   { --theme: var(--amber); }

.c-icon {
  width: 52px;
  height: 52px;
  border-radius: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  font-weight: 800;
  color: #fff;
  background: var(--theme);
  box-shadow: 0 8px 18px color-mix(in srgb, var(--theme) 40%, transparent);
}
.c-body { display: flex; flex-direction: column; gap: 6px; flex: 1; }
.c-code {
  font-size: 12px;
  font-weight: 800;
  color: var(--theme);
  letter-spacing: 1px;
}
.c-title { font-weight: 800; font-size: 17px; }
.c-meta { display: flex; flex-wrap: wrap; gap: 6px; }
.c-meta span {
  font-size: 11px;
  font-weight: 700;
  color: color-mix(in srgb, var(--theme) 90%, #222);
  background: color-mix(in srgb, var(--theme) 12%, #fff);
  border-radius: 999px;
  padding: 2px 9px;
}
.c-desc { font-size: 13px; color: var(--muted); line-height: 1.7; }

.c-enter {
  font-size: 13px;
  font-weight: 700;
  color: var(--theme);
  border: 1px solid color-mix(in srgb, var(--theme) 45%, transparent);
  border-radius: 999px;
  padding: 6px 12px;
  text-align: center;
  transition: all .16s ease;
}
.course-card:hover .c-enter { background: var(--theme); color: #fff; }

.tips {
  margin-top: 26px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 16px 20px;
  box-shadow: var(--shadow-sm);
}
.tips-title { font-weight: 800; margin-bottom: 6px; }
.tips ul { margin: 0; padding-left: 20px; color: var(--muted); font-size: 13px; }
.tips li { margin: 3px 0; }

/* ===== iframe ===== */
.frame {
  display: none;
  width: 100%;
  height: calc(100vh - 52px);
  border: 0;
  background: var(--bg);
}

.site-footer {
  border-top: 1px solid var(--line);
  background: rgba(255, 255, 255, .7);
  padding: 14px;
  text-align: center;
  color: var(--muted);
  font-size: 12px;
}
.site-footer p { margin: 3px 0; }

@media (max-width: 720px) {
  body { font-size: 14px; }
  .frame { height: calc(100vh - 86px); }
  .hero { padding: 40px 14px 34px; }
  .hero h1 { font-size: 26px; }
  .container { padding: 20px 12px 34px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .blob, .course-card::after { animation: none !important; transition: none !important; }
}