:root {
  --paper: #f5efe2;
  --paper-deep: #ebe2d1;
  --ink: #20221f;
  --muted: #6c6b63;
  --faint: #9a9589;
  --rule: #cfc4b1;
  --rule-dark: #a89a84;
  --green: #21483f;
  --green-soft: #dfe9e3;
  --red: #8b3e34;
  --gold: #9a6d25;
  --serif: "Noto Serif SC", "Source Han Serif SC", "Songti SC", SimSun, Georgia, serif;
  --sans: "Inter", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  --mono: "SFMono-Regular", Consolas, monospace;
  --masthead-h: 74px;
  color-scheme: light;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background:
    linear-gradient(90deg, rgba(66, 52, 32, .025) 1px, transparent 1px) 0 0 / 6px 6px,
    var(--paper);
  font-family: var(--serif);
  font-size: 16px;
  line-height: 1.85;
}
button, input { font: inherit; }
a { color: inherit; }
button { color: inherit; }
::selection { color: #fff; background: var(--green); }

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}
.skip-link {
  position: fixed;
  top: -80px;
  left: 24px;
  z-index: 100;
  padding: 8px 12px;
  color: #fff;
  background: var(--green);
}
.skip-link:focus { top: 12px; }

.reading-progress {
  position: fixed;
  inset: 0 0 auto;
  z-index: 60;
  height: 3px;
  background: transparent;
}
.reading-progress span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--red);
  transition: width .12s linear;
}

.masthead {
  position: sticky;
  top: 0;
  z-index: 50;
  display: grid;
  grid-template-columns: 280px minmax(360px, 1fr) 280px;
  min-height: var(--masthead-h);
  background: rgba(245, 239, 226, .96);
  border-bottom: 1px solid var(--rule-dark);
  backdrop-filter: blur(12px);
}
.toc-toggle {
  display: none;
  align-self: center;
  justify-self: start;
  margin-left: 18px;
  padding: 5px 0;
  border: 0;
  border-bottom: 1px solid var(--ink);
  background: transparent;
  cursor: pointer;
}
.site-title {
  grid-column: 2;
  display: inline-flex;
  align-items: baseline;
  gap: 15px;
  justify-self: start;
  align-self: center;
  text-decoration: none;
}
.site-title-main {
  font-size: 22px;
  font-weight: 700;
  letter-spacing: .16em;
}
.site-title-sub {
  color: var(--muted);
  font: 11px/1.4 var(--sans);
  letter-spacing: .09em;
  text-transform: uppercase;
}
.masthead-tools {
  grid-column: 3;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 16px;
  padding-right: 22px;
}
.search-field input {
  width: 180px;
  padding: 7px 0;
  border: 0;
  border-bottom: 1px solid var(--rule-dark);
  outline: none;
  color: var(--ink);
  background: transparent;
  font: 12px/1.4 var(--sans);
}
.search-field input:focus { border-color: var(--green); }
.plain-link, .text-button {
  padding: 2px 0;
  border: 0;
  border-bottom: 1px solid currentColor;
  background: transparent;
  color: var(--green);
  font: 12px/1.4 var(--sans);
  text-decoration: none;
  cursor: pointer;
}

.book-layout {
  display: grid;
  grid-template-columns: 280px minmax(560px, 820px) minmax(220px, 280px);
  justify-content: center;
  min-height: calc(100vh - var(--masthead-h));
}
.book-toc {
  position: sticky;
  top: var(--masthead-h);
  align-self: start;
  height: calc(100vh - var(--masthead-h));
  overflow-y: auto;
  padding: 38px 30px 28px 20px;
  border-right: 1px solid var(--rule);
  scrollbar-width: thin;
}
.toc-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 18px;
}
.toc-head p, .toc-appendix p {
  margin: 0;
  color: var(--faint);
  font: 10px/1.4 var(--sans);
  letter-spacing: .18em;
  text-transform: uppercase;
}
.toc-head button {
  display: none;
  border: 0;
  background: transparent;
  font-size: 24px;
}
.toc-list {
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: toc;
}
.toc-list li { border-top: 1px solid var(--rule); }
.toc-list li:last-child { border-bottom: 1px solid var(--rule); }
.toc-list a {
  display: grid;
  grid-template-columns: 54px 1fr;
  gap: 7px;
  padding: 12px 4px;
  text-decoration: none;
}
.toc-list a span {
  color: var(--faint);
  font: 10px/1.5 var(--sans);
}
.toc-list a strong {
  font-size: 13px;
  font-weight: 600;
  line-height: 1.45;
}
.toc-list a:hover strong,
.toc-list a.is-active strong { color: var(--red); }
.toc-list a.is-active { box-shadow: inset 3px 0 var(--red); padding-left: 11px; }
.toc-appendix { margin-top: 28px; }
.toc-appendix p { margin-bottom: 8px; }
.toc-appendix a {
  display: block;
  padding: 6px 2px;
  color: var(--muted);
  font-size: 12px;
  text-decoration: none;
}
.toc-appendix a:hover, .toc-appendix a.is-active { color: var(--red); }
.toc-foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-top: 30px;
  color: var(--faint);
  font: 10px/1.5 var(--sans);
}

.reading-pane {
  min-width: 0;
  border-right: 1px solid var(--rule);
  outline: none;
}
.book-page {
  min-height: calc(100vh - var(--masthead-h));
  padding: 64px clamp(46px, 7vw, 88px) 100px;
}
.book-page > * { max-width: 690px; margin-left: auto; margin-right: auto; }
.page-kicker {
  margin: 0 0 16px;
  color: var(--red);
  font: 11px/1.4 var(--sans);
  letter-spacing: .14em;
  text-transform: uppercase;
}
.page-title {
  margin: 0;
  font-size: clamp(34px, 5vw, 54px);
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -.04em;
}
.page-subtitle {
  margin: 14px 0 0;
  color: var(--muted);
  font-size: 17px;
  line-height: 1.7;
}
.title-rule {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 14px;
  margin: 30px 0 44px;
  color: var(--faint);
  font: 10px/1 var(--sans);
  letter-spacing: .08em;
}
.title-rule::before, .title-rule::after {
  content: "";
  height: 1px;
  background: var(--rule-dark);
}
.lede {
  margin: 0 0 42px;
  font-size: 19px;
  line-height: 2;
}
.dropcap::first-letter {
  float: left;
  margin: 9px 10px 0 0;
  color: var(--green);
  font-size: 64px;
  font-weight: 700;
  line-height: .75;
}

.cover {
  display: flex;
  min-height: calc(100vh - var(--masthead-h) - 164px);
  flex-direction: column;
  justify-content: center;
}
.cover-mark {
  width: 88px;
  height: 88px;
  margin-bottom: 36px;
  color: var(--green);
  border: 1px solid var(--green);
  font: italic 54px/86px Georgia, serif;
  text-align: center;
  transform: rotate(-2deg);
}
.cover h1 {
  margin: 0;
  font-size: clamp(50px, 8vw, 80px);
  line-height: 1.08;
  letter-spacing: .08em;
}
.cover h1 span {
  display: block;
  margin-top: 12px;
  color: var(--muted);
  font-size: 17px;
  font-weight: 400;
  letter-spacing: .16em;
}
.cover-intro { max-width: 600px; margin: 38px 0 0; font-size: 18px; }
.cover-meta {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0;
  margin-top: 48px;
  border-top: 1px solid var(--rule-dark);
  border-bottom: 1px solid var(--rule-dark);
}
.cover-meta div { padding: 14px 16px 14px 0; }
.cover-meta div + div { padding-left: 16px; border-left: 1px solid var(--rule); }
.cover-meta span { display: block; color: var(--faint); font: 10px/1.4 var(--sans); }
.cover-meta strong { display: block; margin-top: 4px; font-size: 13px; }
.start-reading {
  align-self: flex-start;
  margin-top: 34px;
  color: var(--green);
  font-size: 15px;
  text-decoration-thickness: 1px;
  text-underline-offset: 5px;
}

.chapter-section { margin: 0 0 52px; scroll-margin-top: 94px; }
.chapter-section h2 {
  margin: 0 0 16px;
  padding-top: 12px;
  border-top: 2px solid var(--ink);
  font-size: 25px;
  line-height: 1.45;
}
.chapter-section h3 { margin: 28px 0 9px; font-size: 18px; }
.chapter-section p { margin: 0 0 14px; }
.section-number {
  display: block;
  margin-bottom: 4px;
  color: var(--red);
  font: 10px/1.4 var(--sans);
  letter-spacing: .1em;
}
.method-cue {
  margin: 20px 0 0;
  padding-left: 18px;
  border-left: 2px solid var(--gold);
  color: #5f4c2c;
  font-size: 14px;
}
.formula-list, .step-list, .pitfall-list {
  margin: 14px 0 0;
  padding-left: 1.4em;
}
.formula-list li, .step-list li, .pitfall-list li { margin: 7px 0; }
.formula-list { list-style: none; padding-left: 0; }
.formula-list li { padding: 10px 0; border-bottom: 1px dotted var(--rule-dark); }
.pitfall-list li::marker { color: var(--red); }

.reference-line {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 8px 16px;
  margin: 28px 0 42px;
  padding: 12px 0;
  border-top: 1px solid var(--rule-dark);
  border-bottom: 1px solid var(--rule-dark);
  font-size: 13px;
}
.reference-line span { color: var(--muted); }
.reference-line a { color: var(--green); text-underline-offset: 4px; }

.example, .exercise {
  position: relative;
  margin: 0 0 46px;
  padding-top: 16px;
  border-top: 1px solid var(--rule-dark);
  scroll-margin-top: 100px;
}
.example-label, .exercise-label {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  color: var(--red);
  font: 11px/1.4 var(--sans);
  letter-spacing: .08em;
}
.example-label small, .exercise-label small { color: var(--faint); letter-spacing: 0; }
.example h3, .exercise h3 { margin: 12px 0 14px; font-size: 20px; }
.problem-statement { font-size: 16px; }
.problem-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin: 18px 0 0;
}
.status-button, .inline-button {
  padding: 4px 0;
  border: 0;
  border-bottom: 1px solid var(--rule-dark);
  background: transparent;
  color: var(--muted);
  font: 12px/1.4 var(--sans);
  cursor: pointer;
}
.status-button:hover, .inline-button:hover { color: var(--green); border-color: var(--green); }
.status-button.is-active { color: var(--red); border-color: var(--red); }
details.solution-block {
  margin-top: 15px;
  border-top: 1px dotted var(--rule-dark);
}
details.solution-block summary {
  width: fit-content;
  padding: 9px 0 4px;
  color: var(--green);
  font: 12px/1.4 var(--sans);
  cursor: pointer;
}
.solution-copy { padding: 10px 0 0; }
.solution-copy strong { color: var(--green); }
.trap-note {
  margin-top: 18px;
  padding-left: 16px;
  border-left: 2px solid var(--red);
  color: #6d3d37;
  font-size: 14px;
}
.exercise-index { margin-top: 18px; padding: 0; list-style: none; }
.exercise-index li { display: grid; grid-template-columns: 54px 1fr auto; gap: 10px; padding: 10px 0; border-bottom: 1px dotted var(--rule); }
.exercise-index a { text-decoration: none; }
.exercise-index a:hover { color: var(--red); }
.exercise-index span, .exercise-index small { color: var(--faint); font: 10px/1.5 var(--sans); }

.chapter-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
  margin-top: 70px;
  padding-top: 20px;
  border-top: 1px solid var(--rule-dark);
}
.chapter-nav a { text-decoration: none; }
.chapter-nav a:last-child { text-align: right; }
.chapter-nav span { display: block; color: var(--faint); font: 10px/1.4 var(--sans); }
.chapter-nav strong { font-size: 14px; }
.chapter-nav a:hover strong { color: var(--red); }

.margin-column {
  position: sticky;
  top: var(--masthead-h);
  align-self: start;
  height: calc(100vh - var(--masthead-h));
  overflow-y: auto;
  padding: 58px 24px 36px;
  color: var(--muted);
  scrollbar-width: thin;
}
.margin-note {
  margin-bottom: 34px;
  padding-top: 10px;
  border-top: 1px solid var(--rule-dark);
}
.margin-note h2 {
  margin: 0 0 9px;
  color: var(--ink);
  font: 11px/1.4 var(--sans);
  letter-spacing: .08em;
}
.margin-note p, .margin-note li { margin: 0 0 8px; font-size: 12px; line-height: 1.7; }
.margin-note ul { margin: 0; padding-left: 1.2em; }
.margin-note a { color: var(--green); text-underline-offset: 3px; }
.margin-progress { height: 2px; margin: 12px 0 7px; background: var(--rule); }
.margin-progress span { display: block; height: 100%; background: var(--green); }
.margin-check {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  margin-top: 8px;
  color: var(--ink);
  font: 12px/1.55 var(--sans);
}
.margin-check input { margin-top: 3px; accent-color: var(--green); }

.plan-table, .paper-table {
  width: 100%;
  margin-top: 24px;
  border-collapse: collapse;
  font-size: 13px;
}
.plan-table th, .paper-table th {
  padding: 8px 8px 8px 0;
  border-bottom: 2px solid var(--ink);
  text-align: left;
  font: 11px/1.4 var(--sans);
}
.plan-table td, .paper-table td {
  padding: 12px 8px 12px 0;
  border-bottom: 1px solid var(--rule);
  vertical-align: top;
}
.plan-table td:first-child { color: var(--red); font-family: var(--sans); white-space: nowrap; }
.plan-table td:nth-child(2) { white-space: nowrap; }
.paper-table a { color: var(--green); text-underline-offset: 3px; }

.method-entry, .resource-entry {
  display: grid;
  grid-template-columns: 42px 1fr;
  gap: 14px;
  padding: 18px 0;
  border-top: 1px solid var(--rule);
}
.method-entry:last-child, .resource-entry:last-child { border-bottom: 1px solid var(--rule); }
.method-entry > span, .resource-entry > span { color: var(--red); font: 11px/1.5 var(--sans); }
.method-entry h2, .resource-entry h2 { margin: 0 0 5px; font-size: 18px; }
.method-entry p, .resource-entry p { margin: 0; color: var(--muted); font-size: 14px; }
.method-entry em { display: block; margin-top: 7px; color: var(--green); font-size: 13px; }
.resource-entry a { text-decoration: none; }
.resource-entry a:hover h2 { color: var(--red); }
.resource-group { margin: 40px 0 10px; color: var(--red); font: 11px/1.4 var(--sans); letter-spacing: .12em; }

.pdf-shell { max-width: 880px !important; }
.pdf-intro {
  margin-bottom: 24px;
  padding-bottom: 14px;
  border-bottom: 1px solid var(--rule-dark);
  color: var(--muted);
  font-size: 13px;
}
.pdf-toolbar {
  position: sticky;
  top: calc(var(--masthead-h) + 3px);
  z-index: 10;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  padding: 9px 0;
  background: rgba(245, 239, 226, .97);
  border-bottom: 1px solid var(--rule-dark);
  font: 12px/1.4 var(--sans);
}
.pdf-toolbar button, .file-label {
  padding: 5px 7px;
  border: 1px solid var(--rule-dark);
  background: transparent;
  cursor: pointer;
}
.pdf-toolbar button:hover, .file-label:hover { color: var(--green); border-color: var(--green); }
.pdf-toolbar input[type="number"] {
  width: 62px;
  padding: 5px;
  border: 1px solid var(--rule-dark);
  background: transparent;
}
.file-label input { display: none; }
.pdf-status { margin-left: auto; color: var(--muted); }
.pdf-stage {
  min-height: 640px;
  padding: 24px 0;
  overflow: auto;
  text-align: center;
}
.pdf-stage canvas {
  max-width: 100%;
  height: auto;
  background: #fff;
  box-shadow: 0 4px 18px rgba(55, 42, 24, .13);
}
.pdf-placeholder {
  max-width: 560px;
  margin: 120px auto 0;
  color: var(--muted);
  text-align: left;
}
.pdf-placeholder h2 { color: var(--ink); }
.pdf-placeholder ol { padding-left: 1.2em; }

.search-results {
  position: fixed;
  top: 64px;
  right: 24px;
  z-index: 90;
  width: min(430px, calc(100vw - 48px));
  max-height: 70vh;
  overflow: auto;
  padding: 12px 16px;
  background: #f8f3e8;
  border: 1px solid var(--rule-dark);
}
.search-result { display: block; padding: 10px 0; border-bottom: 1px solid var(--rule); text-decoration: none; }
.search-result:last-child { border-bottom: 0; }
.search-result span { display: block; color: var(--red); font: 10px/1.4 var(--sans); }
.search-result strong { font-size: 14px; }
.search-result small { display: block; color: var(--muted); font-size: 11px; }
.search-empty { color: var(--muted); font-size: 13px; }

.toast {
  position: fixed;
  right: 22px;
  bottom: 22px;
  z-index: 100;
  max-width: 360px;
  padding: 10px 14px;
  color: #fff;
  background: var(--green);
  font: 12px/1.55 var(--sans);
  opacity: 0;
  transform: translateY(12px);
  pointer-events: none;
  transition: .2s ease;
}
.toast.is-visible { opacity: 1; transform: translateY(0); }
.site-footer {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  padding: 15px 24px;
  color: var(--faint);
  border-top: 1px solid var(--rule-dark);
  font: 10px/1.5 var(--sans);
}
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }

@media (max-width: 1180px) {
  .masthead { grid-template-columns: 240px minmax(360px, 1fr) 240px; }
  .book-layout { grid-template-columns: 240px minmax(520px, 780px) 220px; }
  .book-toc { padding-left: 16px; padding-right: 22px; }
  .margin-column { padding-left: 18px; padding-right: 18px; }
  .book-page { padding-left: 46px; padding-right: 46px; }
}

@media (max-width: 980px) {
  .masthead { grid-template-columns: 90px 1fr auto; }
  .toc-toggle { display: block; }
  .site-title { grid-column: 2; }
  .site-title-sub { display: none; }
  .masthead-tools { grid-column: 3; }
  .search-field input { width: 150px; }
  .book-layout { grid-template-columns: minmax(0, 760px) 220px; }
  .book-toc {
    position: fixed;
    inset: var(--masthead-h) auto 0 0;
    z-index: 80;
    width: min(330px, 86vw);
    height: auto;
    background: var(--paper);
    transform: translateX(-102%);
    transition: transform .2s ease;
  }
  .book-toc.is-open { transform: translateX(0); }
  .toc-head button { display: block; cursor: pointer; }
  .toc-scrim {
    position: fixed;
    inset: var(--masthead-h) 0 0;
    z-index: 70;
    background: rgba(28, 25, 19, .35);
  }
  .reading-pane { grid-column: 1; }
  .margin-column { grid-column: 2; }
}

@media (max-width: 760px) {
  :root { --masthead-h: 62px; }
  body { font-size: 15px; }
  .masthead { grid-template-columns: 64px 1fr auto; }
  .toc-toggle { margin-left: 14px; font-size: 12px; }
  .site-title-main { font-size: 17px; letter-spacing: .08em; }
  .masthead-tools { gap: 10px; padding-right: 13px; }
  .search-field { display: none; }
  .plain-link { font-size: 11px; }
  .book-layout { display: block; }
  .reading-pane { border-right: 0; }
  .margin-column { display: none; }
  .book-page { padding: 42px 23px 76px; }
  .page-title { font-size: 36px; }
  .page-subtitle { font-size: 15px; }
  .lede { font-size: 17px; }
  .cover { min-height: calc(100vh - 170px); }
  .cover-mark { width: 68px; height: 68px; font-size: 43px; line-height: 66px; }
  .cover h1 { font-size: 52px; }
  .cover-meta { grid-template-columns: 1fr; }
  .cover-meta div + div { padding-left: 0; border-top: 1px solid var(--rule); border-left: 0; }
  .reference-line { align-items: flex-start; flex-direction: column; }
  .chapter-nav { gap: 12px; }
  .exercise-index li { grid-template-columns: 46px 1fr; }
  .exercise-index small { grid-column: 2; }
  .plan-table { display: block; overflow-x: auto; white-space: nowrap; }
  .plan-table td:last-child { min-width: 330px; white-space: normal; }
  .method-entry, .resource-entry { grid-template-columns: 34px 1fr; }
  .pdf-toolbar { top: var(--masthead-h); }
  .pdf-status { width: 100%; margin-left: 0; }
  .pdf-stage { min-height: 480px; }
  .site-footer { flex-direction: column; gap: 4px; }
}

@media print {
  .masthead, .book-toc, .margin-column, .site-footer, .reading-progress, .chapter-nav, .problem-actions { display: none !important; }
  body { background: #fff; color: #000; }
  .book-layout { display: block; }
  .reading-pane { border: 0; }
  .book-page { padding: 0; }
  details.solution-block > * { display: block; }
}