:root{--ink:#28343c;--muted:#68767d;--accent:#296c68;--line:#dfe5e3;--paper:#fffefa;--font-text:Arial,'Helvetica Neue','PingFang SC','Microsoft YaHei',sans-serif;--size-body:17px;--size-note:14px;--weight-normal:400;--weight-bold:600;color-scheme:light}
*{box-sizing:border-box}
html{scroll-behavior:smooth;scroll-padding-top:24px}
body{margin:0;background:#f1f2ee;color:var(--ink);font:var(--weight-normal) var(--size-body)/1.85 var(--font-text)}
.layout{max-width:1190px;margin:48px auto;display:grid;grid-template-columns:190px minmax(0,1fr);gap:34px;padding:0 24px}
.toc{position:sticky;top:40px;align-self:start;font-size:14px;padding-top:24px}
.toc .label{font-size:11px;letter-spacing:2px;color:var(--muted)}
.toc a{display:block;text-decoration:none;color:var(--muted);padding:12px 0;border-bottom:1px solid var(--line)}
.toc a:hover{color:var(--accent)}
main{background:var(--paper);padding:48px 55px 36px;border:1px solid var(--line);box-shadow:0 6px 30px #23342a05}
.meta{font-size:12px;letter-spacing:1.5px;color:var(--accent);margin:0}
h1{font-size:34px;line-height:1.45;font-weight:var(--weight-bold);letter-spacing:-.5px;margin:14px 0}
header{border-bottom:1px solid var(--line);padding-bottom:26px;margin-bottom:36px}
.lead{color:var(--muted);font-size:16px;margin-bottom:0}
h2{font-size:25px;line-height:1.55;margin:0 0 22px;font-weight:var(--weight-bold)}
h2 .number{color:var(--accent);font-size:15px;display:block;letter-spacing:2px;margin-bottom:8px}
h3{font-size:19px;font-weight:var(--weight-bold);margin:26px 0 10px}
section+section{border-top:1px solid var(--line);padding-top:38px;margin-top:42px}
p{margin:14px 0}
strong{font-weight:var(--weight-bold)}
.question{font-size:var(--size-body);font-weight:var(--weight-bold);margin:18px 0}
.callout{border-left:3px solid var(--accent);padding:14px 20px;background:#eff4f0;margin:24px 0}
.callout p{margin:4px 0}
.tag{font-size:12px;color:var(--accent);letter-spacing:1px;font-weight:var(--weight-bold)}
.with-note{display:grid;grid-template-columns:minmax(0,1fr) 145px;gap:24px;align-items:start}
.sidenote{font-size:var(--size-note);line-height:1.8;color:var(--muted);border-top:2px solid #bacbc5;padding-top:10px;margin-top:18px}
.sidenote strong{font-weight:var(--weight-bold);color:inherit}
table{border-collapse:collapse;width:100%;font-size:var(--size-body);margin:20px 0}
th,td{padding:13px 15px;border-bottom:1px solid var(--line);text-align:left;vertical-align:top}
th{font-size:13px;color:var(--muted);background:#f2f4ee}
td:first-child{width:30%}
.formula{overflow-x:auto;text-align:center;padding:22px 12px;margin:18px 0;background:#f5f5ef;font-family:Georgia,serif;font-size:21px}
.formula math{font-size:1.1em}
details{margin:20px 0;border:1px solid var(--line);padding:0 18px;background:#fff}
summary{cursor:pointer;padding:14px 0;font-size:var(--size-body);color:var(--accent);font-weight:var(--weight-bold)}
details[open]{padding-bottom:12px}
details p{font-size:inherit}
blockquote{font-size:var(--size-note);color:var(--muted);padding-left:18px;border-left:2px solid var(--line);margin:22px 0}
footer{font-size:12px;color:var(--muted);border-top:1px solid var(--line);padding-top:20px;margin-top:40px}
figure{margin:24px 0}
figure img{max-width:100%;height:auto}
figcaption{font-size:13px;color:var(--muted);text-align:center}
.figure-pair{display:grid;grid-template-columns:1fr 1fr;gap:20px}
a:focus-visible,summary:focus-visible{outline:2px solid var(--accent);outline-offset:4px}
@media(max-width:950px){.layout{grid-template-columns:1fr;max-width:850px;margin-top:20px;gap:18px}
.toc{position:static;padding:0;display:flex;gap:20px;flex-wrap:wrap}
.toc a{padding:5px 0}
.toc .label{align-self:center}
main{padding:36px}
}
@media(max-width:600px){:root{--size-body:16px;--size-note:14px}
.layout{padding:0 12px;margin:12px auto}
main{padding:26px 22px}
h1{font-size:27px}
h2{font-size:22px}
.with-note{grid-template-columns:1fr;gap:0}
.sidenote{margin:6px 0 14px;padding:10px 12px;background:#f3f5f0;border-top:0;border-left:2px solid #bacbc5}
.figure-pair{grid-template-columns:1fr}
.formula{font-size:18px}
td,th{padding:10px}
.toc{font-size:12px}
}
@media print{body{background:white;font-size:11pt}
.layout{display:block;margin:0;padding:0;max-width:none}
.toc{display:none}
main{padding:0;border:0;box-shadow:none}
h2,h3,summary{break-after:avoid}
.callout,.formula,figure{break-inside:avoid}
section+section{margin-top:25px;padding-top:25px}
details{border:0}
details:not([open])>*:not(summary){display:block}
summary{list-style:none}
.with-note{grid-template-columns:1fr 130px}
}

/* Reusable semantic colors: keep paragraph text in the shared text color. */
:root {
  --color-setting: #202020;
  --color-definition: #174a82;
  --color-proof: #a3470b;
  --color-example: #32834a;
}
.topic-setting { --topic-color: var(--color-setting); }
.topic-definition { --topic-color: var(--color-definition); }
.topic-proof { --topic-color: var(--color-proof); }
.topic-example { --topic-color: var(--color-example); }
.topic { border-left: 3px solid var(--topic-color); padding-left: 18px; margin: 24px 0; }
.topic h3 { color: var(--topic-color); margin-top: 0; }
.topic-label { color: var(--topic-color); }
.sidenote.topic-example { border-color: var(--color-example); }

.topic-theorem { --topic-color: var(--color-proof); }
.topic-theorem h3 { color: var(--color-proof); }
.topic-proof .topic-example { margin: 22px 0; }
.page-navigation { margin-top: 36px; padding-top: 20px; border-top: 1px solid var(--line); }
.page-navigation a { color: var(--accent); text-decoration: none; }
.page-navigation a:hover { text-decoration: underline; }
.footnotes .formula { background: transparent; font-size: 18px; padding: 12px 0; }
math { font-family: 'STIX Two Math', 'Cambria Math', math; }

/* Separate supplementary material while retaining semantic topic colors. */
section.supplementary { border-top: 3px double var(--line); margin-top: 60px; padding-top: 40px; }
.toc .supplementary-link { margin-top: 24px; border-top: 2px solid var(--line); }
.page-navigation { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 14px 24px; }

/* Shared sidebar: navigate between lectures and within the current page. */
.toc { max-height: calc(100vh - 64px); overflow-y: auto; }
.toc-group + .toc-group { margin-top: 28px; padding-top: 20px; border-top: 1px solid var(--line); }
.toc .label { display: block; margin-bottom: 10px; }
.toc .lecture-link { display: flex; align-items: baseline; gap: 10px; border: 0; border-radius: 6px; padding: 10px 8px; line-height: 1.5; }
.lecture-number { flex: 0 0 20px; font-size: 12px; color: var(--muted); }
.toc .lecture-link[aria-current="page"] { background: #e6eeeb; color: var(--accent); font-weight: var(--weight-bold); }
.toc .lecture-link:hover { background: #edf2ef; }
.toc-local a { padding: 9px 8px; line-height: 1.55; }
.toc .toc-subsection { padding-left: 20px; font-size: 13px; border-bottom: 0; }
.toc .supplementary-link { margin-top: 12px; }
@media(max-width:950px) {
  .toc { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; max-height: none; overflow: visible; }
  .toc-group + .toc-group { margin: 0; padding: 0; border: 0; }
}
@media(max-width:600px) {
  .toc { grid-template-columns: 1fr; gap: 16px; }
  .toc-local { display: flex; flex-wrap: wrap; gap: 6px 16px; }
  .toc-local .label { width: 100%; margin: 0; }
  .toc-local a { border: 0; padding: 4px 0; }
  .toc .toc-subsection { padding-left: 0; }
  .toc .supplementary-link { margin-top: 0; border: 0; }
}

/* Chapter hierarchy shared by all lecture sidebars. */
.toc .lecture-chapter { display: flex; align-items: baseline; gap: 10px; padding: 14px 8px 6px; font-weight: var(--weight-bold); color: var(--ink); line-height: 1.5; }
.toc .lecture-subchapters { margin-left: 8px; padding-left: 6px; border-left: 1px solid var(--line); }
.toc .lecture-subchapters .lecture-number { flex-basis: 32px; }

.toc > .toc-group > .lecture-link { font-weight: var(--weight-bold); color: var(--ink); }
.toc > .toc-group > .lecture-link .lecture-number,
.toc .lecture-chapter .lecture-number { color: inherit; }

/* Shared formula size for the beginner guide; long formulas scroll on narrow screens. */
.beginner-guide .formula { font-size: 14px; }

.beginner-guide .numbered-equation { display: grid; grid-template-columns: minmax(0, 1fr) auto; align-items: center; gap: 16px; }
.beginner-guide .numbered-equation math { overflow-x: auto; }
.beginner-guide .equation-number { font-family: var(--font-text); font-size: 14px; color: var(--muted); }

.beginner-guide .inequality-name { font-weight: var(--weight-bold); color: #174a82; }

.beginner-guide .statistical-term { font-weight: var(--weight-bold); color: #6b412b; }

/* Formal statements in the beginner guide. */
.beginner-guide .theorem-box { border: 1px solid var(--line); border-radius: 0; background: #f5f5ef; padding: 18px 20px; margin: 24px 0; break-inside: avoid; }
.beginner-guide .theorem-box h4 { color: #174a82; font-size: var(--size-body); font-weight: var(--weight-bold); margin: 0 0 12px; }
.beginner-guide .theorem-box p { margin: 10px 0; }
.beginner-guide .theorem-box .formula { background: transparent; margin: 12px 0 0; padding: 12px; }

.beginner-guide .guide-part > h2 { margin-top: 32px; }
.beginner-guide .guide-part + .guide-part { border-top: 1px solid var(--line); padding-top: 38px; margin-top: 42px; }

.beginner-guide .part-placeholder { display: block; padding: 12px 0; color: var(--muted); font-weight: var(--weight-bold); }