/* 一阶倒立摆 RL 教学站 — 视觉：深青绿工程风，非紫白默认 */

:root {
  --bg0: #0c1412;
  --bg1: #13201c;
  --bg2: #1a2e28;
  --ink: #e8f0ec;
  --muted: #9bb5aa;
  --accent: #3dcf9a;
  --accent2: #e8b86d;
  --line: rgba(61, 207, 154, 0.22);
  --danger: #e07a6a;
  --card: rgba(19, 32, 28, 0.85);
  --font-display: "Fraunces", "Source Han Serif SC", "Noto Serif SC", Georgia, serif;
  --font-body: "IBM Plex Sans", "Noto Sans SC", "PingFang SC", sans-serif;
  --font-mono: "IBM Plex Mono", "JetBrains Mono", ui-monospace, monospace;
  --max: 920px;
  --nav-h: 64px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.65;
  background:
    radial-gradient(1200px 600px at 10% -10%, rgba(61, 207, 154, 0.12), transparent 55%),
    radial-gradient(900px 500px at 100% 0%, rgba(232, 184, 109, 0.08), transparent 50%),
    linear-gradient(180deg, var(--bg0), var(--bg1) 40%, var(--bg0));
  min-height: 100vh;
}

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { color: var(--accent2); }

.site-nav {
  position: sticky;
  top: 0;
  z-index: 20;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0 1.25rem;
  backdrop-filter: blur(12px);
  background: rgba(12, 20, 18, 0.82);
  border-bottom: 1px solid var(--line);
}
.brand {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 1.15rem;
  color: var(--ink);
  text-decoration: none;
  margin-right: auto;
  letter-spacing: 0.02em;
}
.brand span { color: var(--accent); }
.site-nav a.nav-link {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.92rem;
  padding: 0.35rem 0.65rem;
  border-radius: 6px;
}
.site-nav a.nav-link:hover,
.site-nav a.nav-link.active {
  color: var(--ink);
  background: rgba(61, 207, 154, 0.12);
}

.wrap {
  width: min(var(--max), calc(100% - 2rem));
  margin: 0 auto;
  padding: 2.5rem 0 4rem;
}

.hero {
  padding: 3.5rem 0 2rem;
  border-bottom: 1px solid var(--line);
  margin-bottom: 2rem;
  animation: rise 0.7s ease both;
}
.hero h1 {
  font-family: var(--font-display);
  font-size: clamp(2rem, 5vw, 3rem);
  font-weight: 600;
  line-height: 1.15;
  margin: 0 0 0.75rem;
  letter-spacing: -0.02em;
}
.hero .lede {
  color: var(--muted);
  font-size: 1.1rem;
  max-width: 38em;
  margin: 0;
}
.hero .meta {
  margin-top: 1.25rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
}
.chip {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--accent);
  border: 1px solid var(--line);
  padding: 0.25rem 0.55rem;
  border-radius: 999px;
  background: rgba(61, 207, 154, 0.06);
}

h2 {
  font-family: var(--font-display);
  font-size: 1.55rem;
  margin: 2.2rem 0 0.8rem;
  font-weight: 600;
}
h3 {
  font-size: 1.15rem;
  margin: 1.6rem 0 0.55rem;
  color: var(--accent2);
  font-weight: 600;
}
p { margin: 0.65rem 0; color: var(--ink); }
.muted { color: var(--muted); }

.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
}
@media (max-width: 720px) {
  .grid-2 { grid-template-columns: 1fr; }
  .site-nav { flex-wrap: wrap; height: auto; padding: 0.6rem 1rem; }
}

.panel {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.15rem 1.25rem;
  animation: rise 0.6s ease both;
}
.panel h3 { margin-top: 0; }
.panel a.cta {
  display: inline-block;
  margin-top: 0.75rem;
  padding: 0.45rem 0.9rem;
  background: var(--accent);
  color: #062018;
  font-weight: 600;
  text-decoration: none;
  border-radius: 8px;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.panel a.cta:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(61, 207, 154, 0.25);
  color: #062018;
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
  margin: 1rem 0;
}
th, td {
  border: 1px solid var(--line);
  padding: 0.55rem 0.7rem;
  text-align: left;
  vertical-align: top;
}
th { background: rgba(61, 207, 154, 0.08); color: var(--accent); font-weight: 600; }

pre, code {
  font-family: var(--font-mono);
  font-size: 0.86rem;
}
pre {
  background: #08110e;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 1rem 1.1rem;
  overflow-x: auto;
  line-height: 1.5;
}
code { color: var(--accent2); }
pre code { color: var(--ink); }

.formula {
  font-family: var(--font-mono);
  background: rgba(232, 184, 109, 0.08);
  border-left: 3px solid var(--accent2);
  padding: 0.85rem 1rem;
  margin: 1rem 0;
  border-radius: 0 8px 8px 0;
  overflow-x: auto;
}

.step-list { counter-reset: step; list-style: none; padding: 0; }
.step-list li {
  counter-increment: step;
  position: relative;
  padding: 0.9rem 0 0.9rem 3rem;
  border-bottom: 1px solid var(--line);
}
.step-list li::before {
  content: counter(step);
  position: absolute;
  left: 0;
  top: 0.95rem;
  width: 1.8rem;
  height: 1.8rem;
  border-radius: 50%;
  background: rgba(61, 207, 154, 0.15);
  color: var(--accent);
  display: grid;
  place-items: center;
  font-family: var(--font-mono);
  font-size: 0.85rem;
}

.pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--line);
}
.pager a {
  text-decoration: none;
  color: var(--muted);
  border: 1px solid var(--line);
  padding: 0.7rem 1rem;
  border-radius: 10px;
  flex: 1;
  transition: border-color 0.2s, color 0.2s;
}
.pager a:hover { border-color: var(--accent); color: var(--ink); }
.pager a.next { text-align: right; }

.figure {
  margin: 1.25rem 0;
  text-align: center;
}
.figure img {
  max-width: 100%;
  border-radius: 10px;
  border: 1px solid var(--line);
  background: #08110e;
}
.figure figcaption {
  color: var(--muted);
  font-size: 0.88rem;
  margin-top: 0.5rem;
}

.footer {
  border-top: 1px solid var(--line);
  padding: 1.5rem;
  text-align: center;
  color: var(--muted);
  font-size: 0.85rem;
}

@keyframes rise {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

.toc a { display: block; padding: 0.25rem 0; color: var(--muted); text-decoration: none; }
.toc a:hover { color: var(--accent); }

.callout {
  border: 1px dashed var(--line);
  border-radius: 10px;
  padding: 1rem 1.15rem;
  margin: 1.25rem 0;
  background: rgba(61, 207, 154, 0.04);
}
.callout strong { color: var(--accent); }