:root {
    --paper: #fbf8f3;
    --paper-raised: #f4efe4;
    --ink: #1c1a16;
    --ink-soft: #5b5347;
    --ink-faint: #8d8271;
    --accent: #b8701a;
    --accent-ink: #7a4a10;
    --accent-soft: #f0dcb8;
    --rule: #e6dfd0;
    --shadow: 0 1px 2px rgba(28, 26, 22, 0.06);
  }

  @media (prefers-color-scheme: dark) {
    :root {
      --paper: #18140f;
      --paper-raised: #221c14;
      --ink: #f1eadc;
      --ink-soft: #b7ac97;
      --ink-faint: #7c7360;
      --accent: #e8a63f;
      --accent-ink: #f4c477;
      --accent-soft: #3a2d18;
      --rule: #342a1c;
      --shadow: 0 1px 2px rgba(0, 0, 0, 0.4);
    }
  }
  :root[data-theme="dark"] {
    --paper: #18140f;
    --paper-raised: #221c14;
    --ink: #f1eadc;
    --ink-soft: #b7ac97;
    --ink-faint: #7c7360;
    --accent: #e8a63f;
    --accent-ink: #f4c477;
    --accent-soft: #3a2d18;
    --rule: #342a1c;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.4);
  }
  :root[data-theme="light"] {
    --paper: #fbf8f3;
    --paper-raised: #f4efe4;
    --ink: #1c1a16;
    --ink-soft: #5b5347;
    --ink-faint: #8d8271;
    --accent: #b8701a;
    --accent-ink: #7a4a10;
    --accent-soft: #f0dcb8;
    --rule: #e6dfd0;
    --shadow: 0 1px 2px rgba(28, 26, 22, 0.06);
  }

  * { box-sizing: border-box; }

  body {
    margin: 0;
    background: var(--paper);
    color: var(--ink);
    font-family: "Noto Sans TC", "PingFang TC", "Microsoft JhengHei", "Hiragino Sans", sans-serif;
    font-size: 16.5px;
    line-height: 1.9;
    -webkit-font-smoothing: antialiased;
  }

  .serif {
    font-family: "Noto Serif TC", "Songti TC", "PMingLiU", "Noto Serif CJK TC", serif;
  }

  .mono {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  }

  main {
    max-width: 42rem;
    margin: 0 auto;
    padding: 5rem 1.5rem 7rem;
  }

  header.masthead {
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    gap: 0.9rem;
    margin-bottom: 4rem;
  }

  .eyebrow {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.72rem;
    letter-spacing: 0.16em;
    color: var(--ink-faint);
    text-transform: uppercase;
  }

  h1.title {
    font-size: 3.6rem;
    font-weight: 700;
    margin: 0;
    line-height: 1;
    text-wrap: balance;
  }

  header.masthead .rule {
    width: 100%;
    height: 1px;
    background: var(--rule);
    margin-top: 0.6rem;
  }

  h2.section {
    font-size: 1.5rem;
    font-weight: 700;
    margin: 3.2rem 0 1.1rem;
    padding-top: 0.2rem;
    color: var(--ink);
    text-wrap: balance;
  }

  .nowrap { white-space: nowrap; }

  h3.subsection {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--accent-ink);
    letter-spacing: 0.02em;
    margin: 2.2rem 0 0.8rem;
  }

  p { margin: 0 0 1.15em; }
  p:last-child { margin-bottom: 0; }

  strong { font-weight: 700; }

  .lede {
    font-size: 1.08rem;
    color: var(--ink-soft);
  }

  blockquote.dialogue {
    margin: 1.8rem 0;
    padding: 1.2rem 1.5rem;
    background: var(--paper-raised);
    border-radius: 3px;
    border-left: 3px solid var(--accent);
    box-shadow: var(--shadow);
  }
  blockquote.dialogue p {
    font-style: italic;
    color: var(--ink-soft);
    margin: 0 0 0.55em;
  }
  blockquote.dialogue p:last-child { margin-bottom: 0; }
  blockquote.dialogue p::before { content: "— "; color: var(--ink-faint); font-style: normal; }

  .pagebreak {
    display: flex;
    align-items: center;
    gap: 0.9rem;
    margin: 3rem 0;
    color: var(--ink-faint);
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.72rem;
    letter-spacing: 0.1em;
  }
  .pagebreak::before, .pagebreak::after {
    content: "";
    flex: 1;
    height: 1px;
    background: var(--rule);
  }

  ul.contributors {
    list-style: none;
    margin: 1.5rem 0;
    padding: 0;
    display: flex;
    flex-direction: column;
    gap: 1.3rem;
  }
  ul.contributors li {
    padding-left: 1.1rem;
    border-left: 2px solid var(--rule);
  }
  ul.contributors .name {
    font-weight: 700;
    color: var(--accent-ink);
  }
  ul.contributors .chap {
    color: var(--ink-faint);
    font-size: 0.88rem;
  }

  .callout {
    display: flex;
    gap: 1rem;
    align-items: flex-start;
    margin: 1.4rem 0;
    padding: 1rem 1.2rem;
    background: var(--paper-raised);
    border-radius: 4px;
    box-shadow: var(--shadow);
  }
  .callout img {
    width: 34px;
    height: 34px;
    flex: none;
    margin-top: 0.1rem;
  }
  .callout p { margin: 0; color: var(--ink-soft); }

  dl.conventions {
    margin: 1.4rem 0;
    display: flex;
    flex-direction: column;
    gap: 0.9rem;
  }
  dl.conventions > div {
    display: grid;
    grid-template-columns: 11rem 1fr;
    gap: 0.6rem 1rem;
    align-items: baseline;
  }
  dl.conventions dt { font-weight: 600; }
  dl.conventions dd { margin: 0; color: var(--ink-soft); }
  dl.conventions dt.italic { font-style: italic; }
  dl.conventions dt.mono { font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace; font-size: 0.92em; }
  dl.conventions dt.mono.bold { font-weight: 700; }
  dl.conventions dt.mono.italic { font-style: italic; }

  address {
    font-style: normal;
    color: var(--ink-soft);
    line-height: 1.85;
    margin: 1.2rem 0;
    padding: 1rem 1.2rem;
    background: var(--paper-raised);
    border-radius: 4px;
    box-shadow: var(--shadow);
  }

  .oreilly-brand {
    display: flex;
    align-items: center;
    gap: 1.1rem;
    margin: 1.4rem 0;
  }
  .oreilly-brand img { width: 90px; flex: none; }
  .oreilly-brand p { margin: 0; color: var(--ink-soft); }

  .signoff {
    margin: 1.6rem 0;
  }
  .signoff h4 {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.88rem;
    color: var(--accent-ink);
    margin: 0 0 0.5rem;
    letter-spacing: 0.02em;
  }
  .signoff p { color: var(--ink-soft); }

  footer.colophon {
    margin-top: 5rem;
    padding-top: 1.6rem;
    border-top: 1px solid var(--rule);
    color: var(--ink-faint);
    font-size: 0.8rem;
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    flex-wrap: wrap;
  }

  a { color: var(--accent-ink); }

  @media (max-width: 640px) {
    h1.title { font-size: 2.6rem; }
    main { padding: 3rem 1.1rem 5rem; }
    dl.conventions > div { grid-template-columns: 1fr; gap: 0.2rem; }
  }

  /* --- chapter reader additions --- */

  nav.chapnav {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    max-width: 42rem;
    margin: 0 auto;
    padding: 1.1rem 1.5rem 0;
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.78rem;
    color: var(--ink-faint);
  }
  nav.chapnav a { color: var(--ink-soft); text-decoration: none; }
  nav.chapnav a:hover { color: var(--accent-ink); }

  .part-label {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.78rem;
    letter-spacing: 0.14em;
    color: var(--accent-ink);
    text-transform: uppercase;
    margin-bottom: 0.3rem;
  }

  ul.plain, ol.plain {
    margin: 0 0 1.15em;
    padding-left: 1.4rem;
    color: var(--ink);
  }
  ul.plain li, ol.plain li { margin-bottom: 0.45em; }
  ul.plain li:last-child, ol.plain li:last-child { margin-bottom: 0; }

  figure.plate {
    margin: 2rem 0;
    text-align: center;
  }
  figure.plate img {
    max-width: 100%;
    border-radius: 4px;
    border: 1px solid var(--rule);
    box-shadow: var(--shadow);
  }
  figure.plate figcaption {
    margin-top: 0.7rem;
    font-size: 0.85rem;
    color: var(--ink-faint);
    line-height: 1.6;
    text-align: left;
  }

  figure.plate figcaption strong { color: var(--ink); font-weight: 700; }

  .table-wrap {
    overflow-x: auto;
    margin-top: 0.6rem;
    border-radius: 4px;
    box-shadow: var(--shadow);
  }
  table.datatable {
    border-collapse: collapse;
    width: 100%;
    font-size: 0.88rem;
    text-align: left;
  }
  table.datatable th, table.datatable td {
    padding: 0.6rem 0.8rem;
    border-bottom: 1px solid var(--rule);
    vertical-align: top;
    overflow-wrap: anywhere;
  }
  table.datatable td:nth-child(2) {
    max-width: 16rem;
  }
  table.datatable thead th {
    background: var(--paper-raised);
    color: var(--accent-ink);
    font-weight: 700;
    white-space: nowrap;
  }
  table.datatable tbody tr:nth-child(even) { background: var(--paper-raised); }
  table.datatable tbody td:first-child { font-weight: 600; }

  pre.code {
    margin: 1.4rem 0;
    padding: 1rem 1.2rem;
    background: var(--paper-raised);
    border-radius: 4px;
    overflow-x: auto;
    box-shadow: var(--shadow);
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.85rem;
    line-height: 1.6;
    color: var(--ink);
    white-space: pre;
  }
  pre.code .tok-keyword { color: var(--accent-ink); font-weight: 600; }
  pre.code .tok-string { color: #4f7942; }
  pre.code .tok-number { color: #2f6f9f; }
  pre.code .tok-comment { color: var(--ink-faint); font-style: italic; }
  @media (prefers-color-scheme: dark) {
    pre.code .tok-string { color: #8fbf7a; }
    pre.code .tok-number { color: #79b6e6; }
  }
  :root[data-theme="dark"] pre.code .tok-string { color: #8fbf7a; }
  :root[data-theme="dark"] pre.code .tok-number { color: #79b6e6; }
  :root[data-theme="light"] pre.code .tok-string { color: #4f7942; }
  :root[data-theme="light"] pre.code .tok-number { color: #2f6f9f; }
  code.inline {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
    font-size: 0.9em;
    background: var(--paper-raised);
    padding: 0.1em 0.35em;
    border-radius: 3px;
  }

  dl.deflist {
    margin: 1.4rem 0;
    padding: 1rem 1.3rem;
    background: var(--paper-raised);
    border-radius: 4px;
    box-shadow: var(--shadow);
  }
  dl.deflist dt {
    font-weight: 700;
    color: var(--accent-ink);
    margin: 1rem 0 0.3rem;
  }
  dl.deflist dt:first-child { margin-top: 0; }
  dl.deflist dd {
    margin: 0 0 0.2rem;
    color: var(--ink-soft);
  }

  .sidebar {
    margin: 1.8rem 0;
    padding: 1.2rem 1.4rem;
    background: var(--paper-raised);
    border-radius: 4px;
    border: 1px solid var(--rule);
  }
  .sidebar .sidebar-title {
    font-weight: 700;
    text-align: center;
    margin-bottom: 0.8rem;
  }
  .sidebar p { color: var(--ink-soft); }

  .fn {
    font-size: 0.85rem;
    color: var(--ink-faint);
    border-top: 1px solid var(--rule);
    margin-top: 2.4rem;
    padding-top: 1rem;
  }
  .fn p { margin-bottom: 0.5em; }

/* --- agentic reliability engineering: callout boxes --- */
.note, .tip, .warning, .example {
  margin: 1.6rem 0;
  padding: 1rem 1.2rem;
  border-radius: 4px;
  box-shadow: var(--shadow);
  font-size: 0.95rem;
}
.note { background: var(--paper-raised); border-left: 3px solid var(--accent); }
.tip { background: var(--paper-raised); border-left: 3px solid #6a9955; }
.warning { background: var(--paper-raised); border-left: 3px solid #c0392b; }
.example { background: var(--paper-raised); border-left: 3px solid #3a7ca5; }
.note .label, .tip .label, .warning .label, .example .label {
  font-weight: 700;
  display: block;
  margin-bottom: 0.4rem;
  color: var(--accent-ink);
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  font-size: 0.82rem;
  letter-spacing: 0.02em;
}
.note p, .tip p, .warning p, .example p { color: var(--ink-soft); margin: 0; }

blockquote {
  margin: 1.8rem 0;
  padding: 1rem 1.4rem;
  background: var(--paper-raised);
  border-left: 3px solid var(--accent);
  border-radius: 3px;
  color: var(--ink-soft);
  font-style: italic;
  box-shadow: var(--shadow);
}