:root {
  color-scheme: light;
  --paper: #f6f5f0;
  --surface: #fffefa;
  --ink: #1d3430;
  --muted: #5a6b65;
  --line: #d5dcd3;
  --accent: #255d4a;
  --soft: #e9eee4;
  --warm: #f2e4c7;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 24px; }
body { margin: 0; background: var(--paper); color: var(--ink); font-family: "Microsoft YaHei", "PingFang SC", "Noto Sans CJK SC", sans-serif; font-size: 16px; line-height: 1.85; }
a { color: inherit; text-underline-offset: 5px; }
a:focus-visible, summary:focus-visible { outline: 3px solid #bc7a26; outline-offset: 5px; }
a:hover { color: var(--accent); }
.skip-link { position: absolute; left: 20px; top: -100px; z-index: 9; background: var(--ink); color: white; padding: 8px 16px; }
.skip-link:focus { top: 12px; }
.preview-bar { padding: 7px 24px; text-align: center; background: var(--warm); color: #634a20; font-size: 12px; letter-spacing: .04em; }
.site-header { max-width: 1160px; margin: auto; padding: 26px 32px; display: flex; align-items: center; justify-content: space-between; gap: 24px; border-bottom: 1px solid var(--line); }
.wordmark { display: inline-flex; align-items: center; gap: 12px; text-decoration: none; flex-shrink: 0; }
.wordmark-symbol { width: 38px; height: 38px; display: grid; place-items: center; color: var(--surface); background: var(--ink); border-radius: 50%; font-size: 21px; }
.wordmark strong { display: block; font-size: 19px; letter-spacing: .03em; line-height: 1.4; }
.wordmark small { display: block; font-size: 10px; color: var(--muted); letter-spacing: .2em; }
.primary-nav { display: flex; flex-wrap: wrap; align-items: center; gap: 9px 24px; }
.primary-nav a { font-size: 13px; text-decoration: none; color: var(--muted); border-bottom: 1px solid transparent; padding: 4px 0; }
.primary-nav a[aria-current="page"] { border-color: var(--ink); color: var(--ink); }
main { max-width: 1160px; padding: 0 32px; margin: auto; }
.hero { max-width: 850px; padding: 66px 0 50px; }
.eyebrow { color: var(--accent); font-size: 12px; letter-spacing: .14em; font-weight: 600; margin: 0 0 16px; }
h1, h2, h3, p { overflow-wrap: anywhere; }
h1 { font-family: "Noto Serif CJK SC", "Source Han Serif SC", "Songti SC", SimSun, serif; font-size: clamp(36px, 4.6vw, 58px); line-height: 1.28; font-weight: 600; letter-spacing: -.035em; margin: 0 0 24px; }
.lead { max-width: 650px; font-size: 17px; line-height: 1.95; color: var(--muted); margin: 0; }
.actions { display: flex; align-items: center; flex-wrap: wrap; gap: 18px 28px; margin: 28px 0 14px; }
.button { display: inline-flex; align-items: center; justify-content: space-between; gap: 25px; background: var(--ink); color: white; text-decoration: none; font-size: 14px; padding: 12px 20px; border-radius: 3px; }
.button:hover { background: var(--accent); color: white; }
.text-link { font-size: 14px; text-decoration: none; border-bottom: 1px solid var(--line); padding: 4px 0; }
.caption { font-size: 12px; color: var(--muted); max-width: 650px; }
.essentials { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); padding: 28px 0; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.essentials > div { padding: 0 26px; border-left: 1px solid var(--line); }
.essentials > div:first-child { padding-left: 0; border-left: 0; }
.essentials > div:last-child { padding-right: 0; }
.number { font-family: Georgia, serif; font-size: 13px; color: var(--accent); }
.essentials h2 { font-size: 17px; margin: 10px 0 8px; }
.essentials p { color: var(--muted); font-size: 14px; margin: 0; }
.section { padding: 56px 0; border-bottom: 1px solid var(--line); }
.section-heading { margin-bottom: 24px; }
.section h2 { font-size: 27px; line-height: 1.5; margin: 0 0 18px; font-weight: 500; }
.section .eyebrow { margin-bottom: 10px; }
.reading-list { border-top: 1px solid var(--line); }
.reading-list > a { display: flex; gap: 24px; padding: 24px 4px; text-decoration: none; border-bottom: 1px solid var(--line); transition: background .15s; }
.reading-list > a:hover { background: var(--soft); }
.reading-list > a:last-child { border-bottom: 0; }
.list-index { color: var(--muted); font-family: Georgia, serif; font-size: 13px; padding-top: 4px; }
.reading-list h3 { font-size: 18px; font-weight: 500; margin: 0 0 3px; }
.reading-list p { font-size: 14px; color: var(--muted); margin: 0; }
.arrow { margin-left: auto; align-self: center; font-size: 23px; }
.identity { display: grid; grid-template-columns: 1fr 2fr; gap: 60px; }
.fact-list { margin: 0; }
.fact-list > div { display: grid; grid-template-columns: 105px minmax(0, 1fr); padding: 16px 0; border-bottom: 1px solid var(--line); }
.fact-list > div:first-child { padding-top: 0; }
.fact-list dt { color: var(--muted); font-size: 13px; }
.fact-list dd { margin: 0; font-size: 14px; overflow-wrap: anywhere; }
.fact-list dd span { display: block; color: var(--muted); font-size: 13px; margin-top: 4px; }
.note { background: var(--soft); border-left: 3px solid #91aa89; padding: 20px 22px; margin-top: 25px; font-size: 14px; }
.note strong { font-size: 14px; }
.note p { margin: 8px 0 0; }
.split-note { display: grid; grid-template-columns: 1fr 2fr; gap: 60px; }
.split-note p { margin-top: 0; color: var(--muted); font-size: 15px; }
.article-header { padding: 56px 0 42px; max-width: 860px; }
.article-header h1 { font-size: clamp(34px, 4.1vw, 51px); }
.article-meta { font-size: 12px; color: var(--muted); margin-top: 18px; }
.article-layout { display: grid; grid-template-columns: 190px minmax(0, 1fr); gap: 56px; border-top: 1px solid var(--line); padding-top: 28px; padding-bottom: 60px; }
.toc { align-self: start; border-right: 1px solid var(--line); padding-right: 22px; position: sticky; top: 24px; }
.toc p { font-size: 11px; color: var(--muted); letter-spacing: .1em; margin: 0 0 12px; }
.toc a { display: block; padding: 7px 0; font-size: 13px; text-decoration: none; }
.article-body { min-width: 0; max-width: 780px; }
.article-body section { margin: 0 0 42px; }
.article-body h2 { font-size: 24px; font-weight: 500; line-height: 1.5; margin: 0 0 20px; }
.article-body h3 { font-size: 17px; font-weight: 600; margin: 0 0 7px; }
.article-body p, .article-body li { font-size: 15px; color: #3e514b; }
.article-body p { margin: 0 0 16px; }
.article-body ul, .article-body ol { padding-left: 24px; }
.article-body li { margin-bottom: 12px; }
.steps { list-style: none; padding: 0 !important; counter-reset: step; }
.steps li { position: relative; counter-increment: step; border-bottom: 1px solid var(--line); padding: 0 0 16px 42px; margin-bottom: 23px; }
.steps li::before { content: counter(step, decimal-leading-zero); position: absolute; left: 0; top: 0; color: var(--accent); font-family: Georgia, serif; }
.table-wrap { overflow-x: auto; margin-bottom: 22px; }
table { width: 100%; border-collapse: collapse; font-size: 14px; line-height: 1.8; }
caption { text-align: left; font-size: 12px; color: var(--muted); padding-bottom: 12px; }
th, td { text-align: left; vertical-align: top; padding: 15px 16px; border-bottom: 1px solid var(--line); overflow-wrap: anywhere; }
thead { background: var(--soft); }
th { font-weight: 500; }
tbody th { min-width: 86px; color: var(--ink); }
.review-note { background: #f5eddc; border-color: #c7a767; }
.article-body .note p { font-size: 14px; margin: 9px 0 0; }
.worked-example { padding: 23px; border: 1px solid var(--line); margin: 23px 0; }
.worked-example > span { font-size: 12px; color: var(--muted); display: block; margin-bottom: 10px; }
.worked-example p { margin: 0; }
.worked-example p + p { margin-top: 12px; }
.example-label { font-size: 12px !important; color: var(--muted) !important; }
.article-body .source-note { margin-top: 26px; font-size: 12px; color: var(--muted); }
.comparison { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin: 24px 0; }
.comparison > div { padding: 25px; background: var(--soft); }
.comparison > div:last-child { background: #eeeee7; }
.comparison span { display: block; color: var(--muted); font-size: 12px; }
.comparison strong { display: block; font-size: 24px; margin: 8px 0; font-weight: 500; }
.comparison p { font-size: 14px; margin: 0; }
.next-read { margin-top: 42px; padding-top: 24px; border-top: 1px solid var(--line); }
.next-read span { display: block; font-size: 12px; color: var(--muted); margin-bottom: 8px; }
.next-read a { font-size: 16px; text-decoration: none; }
.site-footer { max-width: 1160px; margin: auto; padding: 32px; color: var(--muted); font-size: 12px; }
.footer-top { display: flex; justify-content: space-between; flex-wrap: wrap; gap: 14px; margin-bottom: 18px; }
.footer-top strong { color: var(--ink); font-size: 14px; }
.footer-links { display: flex; flex-wrap: wrap; gap: 16px; }
.site-footer p { margin: 6px 0; }
.not-found { padding-top: 80px; padding-bottom: 100px; }
@media (max-width: 820px) {
  .site-header { padding: 20px 24px; align-items: flex-start; flex-direction: column; gap: 15px; }
  .primary-nav { gap: 8px 19px; }
  main { padding: 0 24px; }
  .hero { padding: 44px 0 36px; }
  .identity, .split-note { grid-template-columns: 1fr; gap: 20px; }
  .identity h2 br { display: none; }
  .article-layout { grid-template-columns: 1fr; gap: 28px; }
  .toc { position: static; border-right: 0; padding-right: 0; padding-bottom: 16px; border-bottom: 1px solid var(--line); display: flex; flex-wrap: wrap; gap: 6px 20px; }
  .toc p { flex-basis: 100%; margin-bottom: 2px; }
  .toc a { padding: 3px 0; }
  .site-footer { padding: 28px 24px; }
}
@media (max-width: 540px) {
  .preview-bar { text-align: left; padding: 9px 20px; font-size: 11px; }
  .site-header, .site-footer { padding-left: 20px; padding-right: 20px; }
  main { padding: 0 20px; }
  .primary-nav { gap: 7px 16px; }
  .primary-nav a { font-size: 12px; }
  .lead { font-size: 15px; }
  .hero h1 { margin-bottom: 20px; }
  .actions { gap: 14px 20px; }
  .caption { font-size: 11px; }
  .essentials { grid-template-columns: 1fr; padding: 8px 0; }
  .essentials > div, .essentials > div:first-child, .essentials > div:last-child { position: relative; padding: 18px 0 18px 36px; border-left: 0; border-bottom: 1px solid var(--line); }
  .essentials > div:last-child { border-bottom: 0; }
  .essentials .number { position: absolute; top: 20px; left: 0; }
  .essentials h2 { margin: 0 0 6px; font-size: 16px; }
  .essentials p { font-size: 13px; }
  .section { padding: 36px 0; }
  .section h2 { font-size: 23px; }
  .reading-list > a { gap: 15px; padding: 20px 0; }
  .reading-list h3 { font-size: 16px; }
  .reading-list p { font-size: 13px; }
  .fact-list > div { grid-template-columns: 75px minmax(0, 1fr); }
  .note { padding: 17px; }
  .article-header { padding: 36px 0 28px; }
  .article-meta { font-size: 11px; }
  .article-body h2 { font-size: 21px; }
  .article-body p, .article-body li { font-size: 14px; }
  th, td { padding: 12px 10px; font-size: 12px; }
  tbody th { min-width: 68px; }
  .comparison { grid-template-columns: 1fr; gap: 10px; }
  .comparison > div { padding: 20px; }
  .comparison strong { font-size: 22px; }
}
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } .reading-list > a { transition: none; } }