:root {
  --paper: #f4efe6;
  --paper-2: #fbf8f1;
  --ink: #1c1712;
  --ink-soft: #4a433a;
  --muted: #7a7166;
  --line: #e4dccf;
  --line-strong: #d3c6b4;
  --accent: #b64022;
  --accent-soft: #f3e2d8;
  --pine: #3d5a45;
  --pine-soft: #e7efe8;
  --sidebar: #efe7da;
  --shadow: 0 18px 40px rgba(62, 42, 22, 0.08);
  --mono: "IBM Plex Mono", "Sarasa Mono SC", "Source Code Pro", ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  --sans: "PingFang SC", "Hiragino Sans GB", "Noto Sans SC", "Source Han Sans SC", "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;
  --serif: "Iowan Old Style", Palatino, "Palatino Linotype", "Songti SC", "Noto Serif SC", "Source Han Serif SC", "STSong", serif;
  --sidebar-w: 292px;
  --top: 58px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(1200px 480px at 80% -10%, rgba(182, 64, 34, 0.06), transparent 50%),
    var(--paper);
  font-family: var(--sans);
  font-size: 16.5px;
  line-height: 1.75;
}

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { color: #8d2e14; }

.topbar {
  position: sticky;
  top: 0;
  z-index: 30;
  height: var(--top);
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 0 16px 0 12px;
  background: rgba(244, 239, 230, 0.92);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.menu-btn, .icon-btn {
  appearance: none;
  border: 1px solid var(--line-strong);
  background: var(--paper-2);
  color: var(--ink);
  border-radius: 10px;
  height: 36px;
  padding: 0 12px;
  font: inherit;
  cursor: pointer;
}
.menu-btn { display: none; }
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: inherit;
  text-decoration: none;
  min-width: 0;
}
.seal {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 1.5px solid var(--accent);
  color: var(--accent);
  display: grid;
  place-items: center;
  font-family: var(--serif);
  font-size: 15px;
  flex: none;
}
.brand-text { display: flex; flex-direction: column; line-height: 1.15; min-width: 0; }
.brand-text strong { font-size: 14px; font-weight: 650; letter-spacing: 0.01em; }
.brand-text span { font-size: 12px; color: var(--muted); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.top-links { margin-left: auto; display: flex; gap: 12px; align-items: center; font-size: 13.5px; }
.top-links a { color: var(--ink-soft); text-decoration: none; }
.top-links a:hover { color: var(--accent); }

.layout { display: flex; min-height: calc(100vh - var(--top)); }
.sidebar {
  width: var(--sidebar-w);
  flex: none;
  position: sticky;
  top: var(--top);
  height: calc(100vh - var(--top));
  overflow: auto;
  background: linear-gradient(180deg, #f3e8d8 0%, var(--sidebar) 120px);
  border-right: 1px solid var(--line);
  padding: 14px 12px 28px;
}
.sidebar::-webkit-scrollbar { width: 10px; }
.sidebar::-webkit-scrollbar-thumb { background: #d7cbb8; border-radius: 99px; }

.search {
  position: sticky;
  top: 0;
  z-index: 2;
  background: linear-gradient(#f3e8d8, #f3e8d8 80%, rgba(243, 232, 216, 0));
  padding-bottom: 10px;
}
.search input {
  width: 100%;
  border: 1px solid var(--line-strong);
  background: var(--paper-2);
  border-radius: 12px;
  padding: 9px 12px;
  font: inherit;
  font-size: 14px;
  color: var(--ink);
  outline: none;
}
.search input:focus { border-color: #c9a392; box-shadow: 0 0 0 3px rgba(182, 64, 34, 0.12); }
.search small { display: block; color: var(--muted); font-size: 12px; margin-top: 6px; padding-left: 2px; }

.nav-group { margin: 8px 0 14px; }
.nav-group.is-empty { display: none; }
.nav-head {
  display: flex;
  gap: 8px;
  align-items: baseline;
  padding: 6px 8px 4px;
}
.nav-head a {
  color: var(--ink);
  text-decoration: none;
  font-weight: 650;
  font-size: 13.5px;
}
.nav-head a:hover { color: var(--accent); }
.nav-head .stage {
  margin-left: auto;
  font-size: 11px;
  color: var(--muted);
  letter-spacing: 0.04em;
}
.nav-lesson {
  display: grid;
  grid-template-columns: 28px 1fr;
  gap: 2px 6px;
  padding: 5px 8px;
  border-radius: 10px;
}
.nav-lesson:hover { background: rgba(255, 252, 246, 0.55); }
.nav-lesson.is-hidden { display: none; }
.num {
  font-variant-numeric: tabular-nums;
  color: var(--muted);
  font-size: 12px;
  padding-top: 2px;
}
.lesson-main {
  color: var(--ink);
  text-decoration: none;
  font-size: 13.4px;
  line-height: 1.45;
}
.lesson-main:hover, .lesson-main.is-active { color: var(--accent); }
.lesson-main.is-active { font-weight: 650; }
.nav-lesson.is-current { background: #fffaf4; box-shadow: inset 2px 0 0 var(--accent); }
.sublinks {
  grid-column: 2;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 1px;
}
.sublinks a {
  font-size: 12px;
  color: var(--pine);
  text-decoration: none;
}
.sublinks a:hover, .sublinks a.is-active { text-decoration: underline; }
.sublinks a.is-active { font-weight: 650; }
.nav-section-label {
  grid-column: 1 / -1;
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--muted);
  text-transform: none;
  padding: 8px 8px 2px;
}

.backdrop { display: none; }

.content {
  flex: 1;
  min-width: 0;
  padding: 28px 28px 64px;
}
.article {
  max-width: 760px;
  margin: 0 auto;
}
.kicker {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 12px;
  align-items: center;
  color: var(--muted);
  font-size: 13px;
  margin-bottom: 8px;
}
.kicker a { color: var(--ink-soft); text-decoration: none; }
.kicker a:hover { color: var(--accent); }
.crumb-dot { color: var(--line-strong); }

.article h1 {
  font-family: var(--serif);
  font-weight: 650;
  font-size: 2.05rem;
  line-height: 1.28;
  letter-spacing: -0.01em;
  margin: 0 0 0.6em;
}
.article h2 {
  font-family: var(--serif);
  font-size: 1.45rem;
  line-height: 1.35;
  margin: 1.7em 0 0.55em;
  padding-top: 0.2em;
}
.article h3 { font-size: 1.15rem; margin: 1.4em 0 0.4em; }
.article h4 { font-size: 1.02rem; margin: 1.2em 0 0.35em; }
.article p { margin: 0.75em 0; }
.article strong { font-weight: 680; }
.article hr { border: 0; border-top: 1px solid var(--line); margin: 1.8em 0; }
.article img { max-width: 100%; height: auto; border-radius: 10px; border: 1px solid var(--line); background: white; }
.article ul, .article ol { padding-left: 1.3em; }
.article li { margin: 0.25em 0; }
.article blockquote {
  margin: 1em 0;
  padding: 0.2em 0 0.2em 1em;
  border-left: 3px solid #e0b09a;
  color: var(--ink-soft);
  background: linear-gradient(90deg, rgba(182, 64, 34, 0.05), transparent 80%);
}
.article blockquote p { margin: 0.4em 0; }

.table-wrap { overflow-x: auto; margin: 1em 0 1.2em; border: 1px solid var(--line); border-radius: 12px; background: var(--paper-2); }
.article table { width: 100%; border-collapse: collapse; font-size: 14.5px; line-height: 1.55; }
.article th, .article td { padding: 8px 10px; text-align: left; vertical-align: top; border-bottom: 1px solid var(--line); }
.article th { background: #f3eadc; font-weight: 650; }
.article tr:last-child td { border-bottom: 0; }

.article code {
  font-family: var(--mono);
  font-size: 0.88em;
  background: #efe6d8;
  padding: 0.08em 0.35em;
  border-radius: 5px;
}
.article pre, .article .codehilite {
  background: #fbf8f2;
  border: 1px solid var(--line-strong);
  border-radius: 12px;
  overflow: auto;
  margin: 1em 0 1.15em;
}
.article pre {
  padding: 12px 14px;
  line-height: 1.55;
}
.article .codehilite pre {
  margin: 0;
  border: 0;
  background: transparent;
  padding: 12px 14px;
}
.article pre code, .article .codehilite code {
  background: transparent;
  padding: 0;
  font-size: 13px;
  color: inherit;
}
.article .codehilite { position: relative; }
.pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-top: 2.4em;
}
.pager a {
  display: block;
  text-decoration: none;
  color: var(--ink);
  border: 1px solid var(--line);
  background: var(--paper-2);
  border-radius: 12px;
  padding: 12px 14px;
}
.pager a:hover { border-color: #d7b2a4; }
.pager .dir { display: block; color: var(--muted); font-size: 12px; }
.pager .next { text-align: right; }
.pager .empty { visibility: hidden; }

.page-toc { margin: 0 0 1.2em; border: 1px dashed var(--line-strong); border-radius: 12px; padding: 8px 12px; background: rgba(255,252,246,0.7); }
.page-toc summary { cursor: pointer; color: var(--ink-soft); font-size: 14px; }
.page-toc ul { margin: 0.4em 0 0.2em; padding-left: 1.1em; }
.page-toc a { color: var(--ink-soft); text-decoration: none; font-size: 14px; }
.page-toc a:hover { color: var(--accent); }

.footer {
  max-width: 760px;
  margin: 28px auto 0;
  padding-top: 16px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 13px;
}
.footer a { color: var(--ink-soft); }

.hero { max-width: 980px; margin: 0 auto 18px; }
.hero h1 {
  font-family: var(--serif);
  font-size: clamp(2rem, 4vw, 3.1rem);
  line-height: 1.15;
  margin: 0 0 0.35em;
  letter-spacing: -0.02em;
}
.lede { font-size: 1.12rem; color: var(--ink-soft); max-width: 42em; }
.meta-row { display: flex; flex-wrap: wrap; gap: 8px; margin: 16px 0 8px; }
.chip {
  border: 1px solid var(--line-strong);
  background: var(--paper-2);
  border-radius: 999px;
  padding: 4px 10px;
  font-size: 13px;
  color: var(--ink-soft);
}
.hero-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 16px; }
.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  text-decoration: none;
  border-radius: 12px;
  padding: 9px 14px;
  font-size: 14.5px;
}
.btn-primary { background: var(--ink); color: #f8f3ea; }
.btn-primary:hover { color: white; }
.btn-ghost { border: 1px solid var(--line-strong); color: var(--ink); background: transparent; }
.btn-ghost:hover { border-color: var(--accent); color: var(--accent); }

.section-title {
  max-width: 980px;
  margin: 28px auto 12px;
  display: flex;
  align-items: baseline;
  gap: 10px;
}
.section-title h2 { font-family: var(--serif); font-size: 1.45rem; margin: 0; }
.section-title span { color: var(--muted); font-size: 13px; }

.track-grid, .project-grid {
  max-width: 980px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(270px, 1fr));
  gap: 12px;
}
.card {
  display: flex;
  flex-direction: column;
  gap: 8px;
  text-decoration: none;
  color: inherit;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 14px 14px 13px;
  min-height: 148px;
  box-shadow: 0 1px 0 rgba(255,255,255,0.6) inset;
}
.card:hover { border-color: #d7b2a4; transform: translateY(-1px); }
.card-top { display: flex; gap: 8px; align-items: center; color: var(--muted); font-size: 12px; }
.card h3 { margin: 0; font-size: 1.05rem; line-height: 1.35; font-family: var(--serif); }
.card p { margin: 0; color: var(--ink-soft); font-size: 14px; line-height: 1.55; flex: 1; }
.card .go { color: var(--accent); font-size: 13px; }

.project-card img { width: 100%; height: 140px; object-fit: cover; border-radius: 10px; border: 1px solid var(--line); }

.note {
  max-width: 980px;
  margin: 18px auto 0;
  color: var(--muted);
  font-size: 13.5px;
}

.figures { display: grid; gap: 12px; margin-top: 1.4em; }
.figures figure { margin: 0; }
.figures figcaption { color: var(--muted); font-size: 13px; margin-top: 6px; }

.mermaid { background: white; border: 1px solid var(--line); border-radius: 12px; padding: 10px; overflow-x: auto; }

@media (max-width: 900px) {
  .menu-btn { display: inline-flex; align-items: center; }
  .brand-text span { display: none; }
  .sidebar {
    position: fixed;
    z-index: 40;
    top: 0;
    left: 0;
    height: 100vh;
    transform: translateX(-105%);
    transition: transform 0.18s ease;
    box-shadow: var(--shadow);
    padding-top: 16px;
  }
  body.nav-open .sidebar { transform: none; }
  .backdrop {
    display: block;
    position: fixed;
    inset: 0;
    background: rgba(40, 28, 16, 0.35);
    z-index: 35;
    opacity: 0;
    pointer-events: none;
  }
  body.nav-open .backdrop { opacity: 1; pointer-events: auto; }
  .content { padding: 18px 16px 48px; }
  .top-links .hide-sm { display: none; }
}

@media (min-width: 1180px) {
  .article { max-width: 780px; }
}

pre { line-height: 125%; }
td.linenos .normal { color: inherit; background-color: transparent; padding-left: 5px; padding-right: 5px; }
span.linenos { color: inherit; background-color: transparent; padding-left: 5px; padding-right: 5px; }
td.linenos .special { color: #000000; background-color: #ffffc0; padding-left: 5px; padding-right: 5px; }
span.linenos.special { color: #000000; background-color: #ffffc0; padding-left: 5px; padding-right: 5px; }
.codehilite .hll { background-color: #ffffcc }
.codehilite { background: #f8f8f8; }
.codehilite .c { color: #8F5902; font-style: italic } /* Comment */
.codehilite .err { color: #A40000; border: 1px solid #EF2929 } /* Error */
.codehilite .g { color: #000 } /* Generic */
.codehilite .k { color: #204A87; font-weight: bold } /* Keyword */
.codehilite .l { color: #000 } /* Literal */
.codehilite .n { color: #000 } /* Name */
.codehilite .o { color: #CE5C00; font-weight: bold } /* Operator */
.codehilite .x { color: #000 } /* Other */
.codehilite .p { color: #000; font-weight: bold } /* Punctuation */
.codehilite .ch { color: #8F5902; font-style: italic } /* Comment.Hashbang */
.codehilite .cm { color: #8F5902; font-style: italic } /* Comment.Multiline */
.codehilite .cp { color: #8F5902; font-style: italic } /* Comment.Preproc */
.codehilite .cpf { color: #8F5902; font-style: italic } /* Comment.PreprocFile */
.codehilite .c1 { color: #8F5902; font-style: italic } /* Comment.Single */
.codehilite .cs { color: #8F5902; font-style: italic } /* Comment.Special */
.codehilite .gd { color: #A40000 } /* Generic.Deleted */
.codehilite .ge { color: #000; font-style: italic } /* Generic.Emph */
.codehilite .ges { color: #000; font-weight: bold; font-style: italic } /* Generic.EmphStrong */
.codehilite .gr { color: #EF2929 } /* Generic.Error */
.codehilite .gh { color: #000080; font-weight: bold } /* Generic.Heading */
.codehilite .gi { color: #00A000 } /* Generic.Inserted */
.codehilite .go { color: #000; font-style: italic } /* Generic.Output */
.codehilite .gp { color: #8F5902 } /* Generic.Prompt */
.codehilite .gs { color: #000; font-weight: bold } /* Generic.Strong */
.codehilite .gu { color: #800080; font-weight: bold } /* Generic.Subheading */
.codehilite .gt { color: #A40000; font-weight: bold } /* Generic.Traceback */
.codehilite .kc { color: #204A87; font-weight: bold } /* Keyword.Constant */
.codehilite .kd { color: #204A87; font-weight: bold } /* Keyword.Declaration */
.codehilite .kn { color: #204A87; font-weight: bold } /* Keyword.Namespace */
.codehilite .kp { color: #204A87; font-weight: bold } /* Keyword.Pseudo */
.codehilite .kr { color: #204A87; font-weight: bold } /* Keyword.Reserved */
.codehilite .kt { color: #204A87; font-weight: bold } /* Keyword.Type */
.codehilite .ld { color: #000 } /* Literal.Date */
.codehilite .m { color: #0000CF; font-weight: bold } /* Literal.Number */
.codehilite .s { color: #4E9A06 } /* Literal.String */
.codehilite .na { color: #C4A000 } /* Name.Attribute */
.codehilite .nb { color: #204A87 } /* Name.Builtin */
.codehilite .nc { color: #000 } /* Name.Class */
.codehilite .no { color: #000 } /* Name.Constant */
.codehilite .nd { color: #5C35CC; font-weight: bold } /* Name.Decorator */
.codehilite .ni { color: #CE5C00 } /* Name.Entity */
.codehilite .ne { color: #C00; font-weight: bold } /* Name.Exception */
.codehilite .nf { color: #000 } /* Name.Function */
.codehilite .nl { color: #F57900 } /* Name.Label */
.codehilite .nn { color: #000 } /* Name.Namespace */
.codehilite .nx { color: #000 } /* Name.Other */
.codehilite .py { color: #000 } /* Name.Property */
.codehilite .nt { color: #204A87; font-weight: bold } /* Name.Tag */
.codehilite .nv { color: #000 } /* Name.Variable */
.codehilite .ow { color: #204A87; font-weight: bold } /* Operator.Word */
.codehilite .pm { color: #000; font-weight: bold } /* Punctuation.Marker */
.codehilite .w { color: #F8F8F8 } /* Text.Whitespace */
.codehilite .mb { color: #0000CF; font-weight: bold } /* Literal.Number.Bin */
.codehilite .mf { color: #0000CF; font-weight: bold } /* Literal.Number.Float */
.codehilite .mh { color: #0000CF; font-weight: bold } /* Literal.Number.Hex */
.codehilite .mi { color: #0000CF; font-weight: bold } /* Literal.Number.Integer */
.codehilite .mo { color: #0000CF; font-weight: bold } /* Literal.Number.Oct */
.codehilite .sa { color: #4E9A06 } /* Literal.String.Affix */
.codehilite .sb { color: #4E9A06 } /* Literal.String.Backtick */
.codehilite .sc { color: #4E9A06 } /* Literal.String.Char */
.codehilite .dl { color: #4E9A06 } /* Literal.String.Delimiter */
.codehilite .sd { color: #8F5902; font-style: italic } /* Literal.String.Doc */
.codehilite .s2 { color: #4E9A06 } /* Literal.String.Double */
.codehilite .se { color: #4E9A06 } /* Literal.String.Escape */
.codehilite .sh { color: #4E9A06 } /* Literal.String.Heredoc */
.codehilite .si { color: #4E9A06 } /* Literal.String.Interpol */
.codehilite .sx { color: #4E9A06 } /* Literal.String.Other */
.codehilite .sr { color: #4E9A06 } /* Literal.String.Regex */
.codehilite .s1 { color: #4E9A06 } /* Literal.String.Single */
.codehilite .ss { color: #4E9A06 } /* Literal.String.Symbol */
.codehilite .bp { color: #3465A4 } /* Name.Builtin.Pseudo */
.codehilite .fm { color: #000 } /* Name.Function.Magic */
.codehilite .vc { color: #000 } /* Name.Variable.Class */
.codehilite .vg { color: #000 } /* Name.Variable.Global */
.codehilite .vi { color: #000 } /* Name.Variable.Instance */
.codehilite .vm { color: #000 } /* Name.Variable.Magic */
.codehilite .il { color: #0000CF; font-weight: bold } /* Literal.Number.Integer.Long */