:root {
  --bg: #f5f4ef;
  --surface: #fffef9;
  --surface-muted: #eceae2;
  --ink: #1f2521;
  --muted: #657067;
  --accent: #176b52;
  --accent-strong: #0f513e;
  --accent-soft: #dceee7;
  --line: #d8d8cf;
  --code: #f0eee7;
  --shadow: 0 16px 48px rgba(26, 45, 36, 0.08);
  --sidebar: 320px;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  text-rendering: optimizeLegibility;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--bg);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  line-height: 1.75;
}

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

.skip-link {
  position: fixed;
  left: 1rem;
  top: -4rem;
  z-index: 100;
  padding: .6rem 1rem;
  background: var(--ink);
  color: white;
  border-radius: .4rem;
}
.skip-link:focus { top: 1rem; }

.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 20;
  height: 64px;
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0 1.4rem;
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px);
}

.brand {
  color: var(--ink);
  font-family: ui-serif, "Songti SC", "STSong", serif;
  font-size: 1.12rem;
  font-weight: 700;
  text-decoration: none;
  letter-spacing: .03em;
}

.chapter-count { margin-left: auto; color: var(--muted); font-size: .86rem; }
.nav-toggle { display: none; }

.layout { display: grid; grid-template-columns: var(--sidebar) minmax(0, 1fr); padding-top: 64px; }

.sidebar {
  position: fixed;
  top: 64px;
  bottom: 0;
  width: var(--sidebar);
  overflow-y: auto;
  padding: 1.25rem 1rem 3rem;
  background: var(--surface);
  border-right: 1px solid var(--line);
}

.search-wrap { position: sticky; top: -1.25rem; z-index: 2; padding: 1.25rem 0 .8rem; background: var(--surface); }
.search-wrap label { display: block; margin-bottom: .35rem; color: var(--muted); font-size: .8rem; font-weight: 700; }
.search-wrap input {
  width: 100%;
  padding: .68rem .8rem;
  border: 1px solid var(--line);
  border-radius: .55rem;
  color: var(--ink);
  background: var(--bg);
  font: inherit;
  font-size: .9rem;
}
.search-wrap input:focus { outline: 3px solid var(--accent-soft); border-color: var(--accent); }
.search-status { min-height: 1.2em; margin: .25rem 0 0; color: var(--muted); font-size: .76rem; }

.nav-group { margin: 1rem 0 1.4rem; }
.nav-group h2 { margin: 0 0 .4rem .55rem; color: var(--muted); font-size: .76rem; letter-spacing: .08em; }
.nav-group ul { margin: 0; padding: 0; list-style: none; }
.nav-group a {
  display: block;
  padding: .42rem .55rem;
  border-radius: .4rem;
  color: var(--ink);
  font-size: .83rem;
  line-height: 1.42;
  text-decoration: none;
}
.nav-group a:hover { background: var(--surface-muted); }
.nav-group a.active { color: var(--accent-strong); background: var(--accent-soft); font-weight: 700; }
.nav-group li[hidden], .nav-group[hidden] { display: none; }

.content {
  grid-column: 2;
  width: min(100%, 1040px);
  margin: 0 auto;
  padding: 3rem clamp(1.4rem, 5vw, 5rem) 5rem;
}

.article {
  max-width: 780px;
  margin: 0 auto;
  padding: clamp(1.5rem, 4vw, 3.5rem);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 1rem;
  box-shadow: var(--shadow);
}

.article > h1:first-child { margin-top: 0; font-size: clamp(2rem, 5vw, 3rem); line-height: 1.2; }
.article h1, .article h2, .article h3 { font-family: ui-serif, "Songti SC", "STSong", serif; line-height: 1.35; scroll-margin-top: 88px; }
.article h2 { margin-top: 2.5rem; padding-top: .2rem; font-size: 1.5rem; }
.article h3 { margin-top: 1.8rem; font-size: 1.18rem; }
.article p { margin: 1rem 0; }
.article blockquote { margin: 1.5rem 0; padding: .7rem 1.1rem; border-left: 4px solid var(--accent); background: var(--accent-soft); }
.article blockquote p { margin: 0; }
.article ul, .article ol { padding-left: 1.5rem; }
.article li + li { margin-top: .3rem; }
.article hr { border: 0; border-top: 1px solid var(--line); margin: 2.5rem 0; }
.article code { padding: .14rem .34rem; border-radius: .3rem; background: var(--code); font-family: ui-monospace, SFMono-Regular, Menlo, monospace; font-size: .9em; }
.article pre { overflow-x: auto; padding: 1rem; border-radius: .65rem; background: #202820; color: #f4f5ef; }
.article pre code { padding: 0; background: transparent; }
.article table { width: 100%; border-collapse: collapse; margin: 1.4rem 0; font-size: .92rem; }
.article th, .article td { padding: .62rem .7rem; border: 1px solid var(--line); text-align: left; vertical-align: top; }
.article th { background: var(--surface-muted); }

.katex-display { max-width: 100%; margin: 1.5rem 0 !important; padding: .5rem 0; overflow-x: auto; overflow-y: hidden; }
.katex { font-size: 1.06em; }
.math-error { display: inline-block; padding: .2rem .4rem; color: #8b1e1e; background: #ffe6e6; font-family: monospace; }

.hero {
  max-width: 940px;
  margin: 0 auto 2rem;
  padding: clamp(2rem, 6vw, 5rem);
  border-radius: 1rem;
  color: #eefbf5;
  background: radial-gradient(circle at 85% 15%, #3aa67f 0, transparent 34%), linear-gradient(135deg, #113e31, #176b52 60%, #0f513e);
  box-shadow: var(--shadow);
}
.hero .eyebrow { margin: 0 0 .8rem; color: #bfe8d7; font-size: .8rem; font-weight: 800; letter-spacing: .16em; }
.hero h1 { max-width: 760px; margin: 0; font-family: ui-serif, "Songti SC", "STSong", serif; font-size: clamp(2.3rem, 6vw, 4.6rem); line-height: 1.08; }
.hero > p:not(.eyebrow) { max-width: 620px; margin: 1.2rem 0 1.7rem; color: #d8eee5; font-size: 1.08rem; }
.start-button { display: inline-block; padding: .78rem 1.1rem; border-radius: .55rem; color: #124332; background: #f1fbf6; font-weight: 800; text-decoration: none; }

.home .article { margin-top: 2rem; }
.volume-section { max-width: 940px; margin: 2.5rem auto 0; }
.volume-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; }
.volume-card { display: grid; gap: .25rem; min-height: 150px; padding: 1.2rem; border: 1px solid var(--line); border-radius: .8rem; color: var(--ink); background: var(--surface); text-decoration: none; box-shadow: var(--shadow); }
.volume-card:hover { transform: translateY(-2px); border-color: var(--accent); }
.volume-card span { color: var(--accent); font-weight: 800; }
.volume-card strong { align-self: center; font-family: ui-serif, "Songti SC", "STSong", serif; font-size: 1.1rem; }
.volume-card small { align-self: end; color: var(--muted); }

.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; max-width: 780px; margin: 1.5rem auto 0; }
.pager-link { display: grid; gap: .2rem; padding: 1rem; border: 1px solid var(--line); border-radius: .7rem; color: var(--ink); background: var(--surface); text-decoration: none; }
.pager-link span { color: var(--muted); font-size: .76rem; }
.pager-link.next { text-align: right; }
.footer { max-width: 780px; margin: 2.2rem auto 0; color: var(--muted); font-size: .8rem; text-align: center; }

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #111713;
    --surface: #18201b;
    --surface-muted: #232d27;
    --ink: #e7eee9;
    --muted: #a0afa5;
    --accent: #72d4ad;
    --accent-strong: #a1e7cb;
    --accent-soft: #214638;
    --line: #344139;
    --code: #28332c;
    --shadow: 0 16px 48px rgba(0, 0, 0, .22);
  }
}

@media (max-width: 900px) {
  .topbar { padding: 0 .9rem; }
  .nav-toggle { display: inline-flex; align-items: center; padding: .4rem .65rem; border: 1px solid var(--line); border-radius: .4rem; color: var(--ink); background: var(--surface); font: inherit; }
  .chapter-count { display: none; }
  .layout { display: block; }
  .sidebar { z-index: 15; transform: translateX(-105%); transition: transform .2s ease; box-shadow: var(--shadow); }
  body.nav-open { overflow: hidden; }
  body.nav-open .sidebar { transform: translateX(0); }
  .content { width: 100%; padding: 1.2rem .8rem 3rem; }
  .article { padding: 1.4rem 1.1rem; border-radius: .75rem; }
  .volume-grid { grid-template-columns: 1fr; }
  .pager { grid-template-columns: 1fr; }
  .pager-link.next { text-align: left; }
}

@media print {
  .topbar, .sidebar, .pager, .footer { display: none !important; }
  .layout, .content { display: block; width: 100%; padding: 0; margin: 0; }
  .article { max-width: none; padding: 0; border: 0; box-shadow: none; }
}