/* Paper/charcoal publication palette. Controls: 4px; search dialog: 12px. */
:root {
  color-scheme:light;
  --bg:#f6f2e9; --panel:#eee9df; --text:#292a2c; --muted:#66645f;
  --line:#dcd6cb; --accent:#344d67; --code:#ede9e1;
  --syntax-keyword:#8d3343; --syntax-string:#344d67; --syntax-number:#714b27;
  --sans:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;
  --book:"Iowan Old Style","Palatino Linotype","Book Antiqua",Georgia,"Songti SC","Noto Serif CJK SC",serif;
  font:16px/1.7 var(--sans); scroll-padding-top:108px;
}
@media(prefers-color-scheme:dark) {
  :root:not([data-theme=light]) {
    color-scheme:dark; --bg:#202123; --panel:#28292c; --text:#e6e2da; --muted:#b5b1a9;
    --line:#414145; --accent:#b3c5dd; --code:#28292c;
    --syntax-keyword:#e9aebb; --syntax-string:#b3c5dd; --syntax-number:#dfbf95;
  }
}
:root[data-theme=dark] {
  color-scheme:dark; --bg:#202123; --panel:#28292c; --text:#e6e2da; --muted:#b5b1a9;
  --line:#414145; --accent:#b3c5dd; --code:#28292c;
  --syntax-keyword:#e9aebb; --syntax-string:#b3c5dd; --syntax-number:#dfbf95;
}
*{box-sizing:border-box} body{margin:0;background:var(--bg);color:var(--text)}
a{color:var(--accent);text-underline-offset:5px} button,input{font:inherit}
button{cursor:pointer;color:var(--text);background:transparent;border:1px solid var(--line);border-radius:4px;padding:7px 12px;white-space:nowrap}
button:hover{background:var(--panel)} button:active{transform:translateY(1px)}
[hidden]{display:none!important}
button:focus-visible,a:focus-visible,summary:focus-visible,input:focus-visible,pre:focus-visible{outline:2px solid var(--accent);outline-offset:4px}
.skip{position:fixed;top:-100px;background:var(--bg);padding:12px;z-index:5}.skip:focus{top:8px}
.reader-header{position:sticky;top:0;z-index:2;display:flex;align-items:center;justify-content:space-between;height:78px;padding:0 40px;background:var(--bg);border-bottom:1px solid var(--line);gap:20px}
.brand{display:flex;align-items:center;gap:13px;text-decoration:none;color:var(--text);font-size:19px;font-weight:600;letter-spacing:-.5px;line-height:1.2}
.brand small{display:block;font:10px/1.3 var(--sans);letter-spacing:1.5px;color:var(--muted);margin-top:5px}
.brand-mark{display:grid;place-items:center;width:33px;height:38px;border:1px solid var(--text);color:var(--text);font:13px/1 var(--book);letter-spacing:-1px}
.header-actions{display:flex;align-items:center;gap:22px;font-size:12px}
.header-actions a{text-decoration:none;color:var(--text)}
.search-toggle{border-color:transparent;color:var(--muted)}
kbd{font:11px var(--sans);border:1px solid var(--line);border-radius:3px;padding:0 5px;margin-left:30px}
.theme-toggle{font-size:12px;padding:6px 10px;color:var(--muted)}
.reader-layout{max-width:1512px;margin:auto;display:grid;grid-template-columns:220px minmax(0,730px) 180px;justify-content:center;gap:54px;padding:0 40px}
.chapter-nav{position:sticky;top:78px;height:calc(100dvh - 78px);overflow-y:auto;padding:42px 12px 40px 0;font-size:12px;scrollbar-width:thin}
.reader-home{font-size:13px;font-weight:600;text-decoration:none;display:block;margin:0 0 30px;color:var(--text)!important}
.chapter-nav details{margin-bottom:19px}
.chapter-nav summary{cursor:pointer;font-weight:500;line-height:1.65;padding:4px 0;color:var(--muted)}
.chapter-nav details[open]>summary{color:var(--text)}
.chapter-nav ol{padding-left:25px;margin:14px 0}.chapter-nav ul{list-style:none;padding-left:8px}
.chapter-nav li{padding:5px 0 5px 3px;color:var(--muted);line-height:1.65}
.chapter-nav a{color:var(--muted);text-decoration:none}.chapter-nav a:hover{color:var(--text)}
.chapter-nav [aria-current=page]{color:var(--accent);font-weight:650}
.chapter-nav li:has([aria-current=page]){border-right:2px solid var(--accent)}
.nav-resources{border-top:1px solid var(--line);margin-top:30px;padding-top:22px;display:grid;gap:13px;font-size:11px}
main{min-width:0;padding:43px 0 0}
.reading-context{display:flex;justify-content:space-between;font-size:11px;color:var(--muted);margin-bottom:45px;letter-spacing:.04em}
.reading-context a{text-decoration:none;color:var(--muted)}
/* A textbook benefits from a book serif; navigation and code remain in their own families. */
.prose{font:19px/1.9 var(--book);overflow-wrap:break-word}
:lang(zh-CN) .prose{font-size:18px;line-height:2}
.prose h1{font:500 clamp(34px,3.5vw,49px)/1.3 var(--book);letter-spacing:-.035em;margin:0 0 30px;text-wrap:balance}
.prose h2{font:500 29px/1.5 var(--book);letter-spacing:-.025em;margin:58px 0 22px;padding-top:27px;border-top:1px solid var(--line)}
.prose h3{font:600 20px/1.55 var(--sans);margin:37px 0 16px}
.prose h4{font:600 17px/1.6 var(--sans);margin:28px 0 12px}
.prose p{margin:19px 0}.prose li{margin:9px 0}.prose li>p{margin:10px 0}
.prose strong{font-weight:650}
.prose blockquote{border-left:2px solid var(--accent);padding:0 0 0 24px;margin:30px 0;color:var(--muted);font:15px/1.95 var(--sans)}
.prose blockquote p{margin:10px 0}
.chapter-heading{margin:0 0 40px;padding:0 0 32px;border-bottom:1px solid var(--line)}
.prose .chapter-number{font:11px/1.5 var(--sans);color:var(--muted);letter-spacing:.13em;margin:0 0 20px}
.chapter-number span{letter-spacing:0;margin-left:12px}
.chapter-heading h1{margin:0}
.prose img{display:block;max-width:100%;height:auto;margin:34px auto;background:#f7f9f8}
.prose table{display:block;overflow-x:auto;border-collapse:collapse;max-width:100%;font:13px/1.75 var(--sans);margin:28px 0}
.prose th,.prose td{padding:12px 14px;text-align:left;border-bottom:1px solid var(--line);vertical-align:top;min-width:80px}
.prose th{background:var(--panel);font-weight:600}
.prose pre{overflow-x:auto;background:var(--code);border:1px solid var(--line);padding:22px 24px;font:13px/1.9 ui-monospace,SFMono-Regular,Consolas,monospace;tab-size:4;border-radius:0;margin:28px 0}
.prose code{font:.8em/1.7 ui-monospace,SFMono-Regular,Consolas,monospace;overflow-wrap:anywhere}
.prose :not(pre)>code{background:var(--code);padding:2px 4px}.prose pre code{font:inherit;overflow-wrap:normal}
.prose .code-copy{display:block;margin:-16px 0 24px auto;font:11px var(--sans);padding:4px 8px}
.prose .katex{font-size:1.03em;color:var(--text)}.prose eq{display:inline-block;max-width:100%;overflow-x:auto;overflow-y:hidden;vertical-align:middle;padding:2px 0}
.prose eqn,.prose .katex-display{display:block;max-width:100%;overflow-x:auto;overflow-y:hidden;padding:8px 0;margin:24px 0}
.prose .katex-display>.katex{white-space:nowrap}.prose eqn .katex-display{margin:0;padding:0}.prose section{min-width:0}
.prose hr{border:0;border-top:1px solid var(--line);margin:40px 0}
.page-toc{position:sticky;top:125px;height:calc(100dvh - 160px);overflow:auto;font-size:11px;line-height:1.7;scrollbar-width:thin}
.page-toc summary{font-weight:500;color:var(--text);margin-bottom:20px;cursor:pointer}
.page-toc ul{padding:0;list-style:none;border-left:1px solid var(--line)}
.page-toc li{margin:12px 0;padding-left:16px}.page-toc .h3{padding-left:25px}
.page-toc a{color:var(--muted);text-decoration:none}.page-toc a:hover,.page-toc a[aria-current=true]{color:var(--accent)}
.page-turn{display:grid;grid-template-columns:1fr 1fr;gap:36px;border-top:1px solid var(--line);margin-top:70px;padding-top:28px;font-size:14px}
.page-turn a{text-decoration:none}.page-turn a:last-child{text-align:right}
.page-turn small{display:block;color:var(--muted);margin-bottom:10px;font-size:11px}
footer{display:flex;flex-wrap:wrap;gap:12px 22px;justify-content:space-between;font-size:10px;color:var(--muted);border-top:1px solid var(--line);padding:27px 0;margin-top:50px}footer a{color:var(--muted)}
.prose .lead{font:17px/1.85 var(--sans);color:var(--muted);max-width:36em;margin-bottom:30px}
.overview-heading{padding:0 0 32px;margin:0 0 30px;border-bottom:1px solid var(--line)}
.overview-heading h1{font-size:clamp(38px,4vw,57px);max-width:100%}
.overview-heading .start-link{display:inline-block;padding:10px 19px;background:var(--accent);color:var(--bg);border-radius:4px;text-decoration:none;font:13px var(--sans)}
.course-index{display:grid;grid-template-columns:repeat(3,1fr);margin:36px 0 30px;border-block:1px solid var(--line)}
.course-index a{display:block;text-decoration:none;padding:24px 18px 24px 0;font:12px/1.7 var(--sans);color:var(--muted)}
.course-index strong{display:block;color:var(--text);font:34px/1.2 var(--book);margin-bottom:10px}
.course-index a+a{border-left:1px solid var(--line);padding-left:22px}
.prose .edition-note{font:12px/1.85 var(--sans);color:var(--muted);margin:28px 0}
.search-dialog{width:min(720px,calc(100% - 32px));max-height:80dvh;position:fixed;top:10dvh;margin:0 auto;padding:30px;background:var(--bg);color:var(--text);border:1px solid var(--line);border-radius:12px}
.search-dialog::backdrop{background:rgb(0 0 0/.5)}
.search-dialog form{display:flex;justify-content:space-between;align-items:center;gap:20px}
.search-dialog h2{font:500 26px/1.4 var(--book);margin:0 0 18px}
.search-dialog label{display:block;font-size:12px;margin:10px 0;color:var(--muted)}
.search-dialog input{width:100%;padding:12px;border:1px solid var(--accent);border-radius:4px;color:var(--text);background:var(--bg)}
#search-status{font-size:12px;color:var(--muted)}#search-results{padding-left:24px}
#search-results li{margin:24px 0}#search-results a{font-weight:500;font-size:15px}
#search-results p{font-size:12px;line-height:1.85;color:var(--muted);margin:8px 0}
.prose pre [class*=hljs]{color:var(--text)}
.prose pre .hljs-comment,.prose pre .hljs-quote{color:var(--muted)}
.prose pre .hljs-keyword,.prose pre .hljs-selector-tag{color:var(--syntax-keyword)}
.prose pre .hljs-string,.prose pre .hljs-title{color:var(--syntax-string)}
.prose pre .hljs-number,.prose pre .hljs-literal{color:var(--syntax-number)}
.mobile-toc,.mobile-theme{display:none}
@media(min-width:768px){.menu-toggle{display:none!important}}
@media(max-width:1279px){
  .reader-layout{grid-template-columns:205px minmax(0,730px);gap:40px;padding:0 30px}
  .page-toc{display:none}.mobile-toc{display:block;font-size:12px;color:var(--muted);margin:0 0 28px}
  .mobile-toc summary{cursor:pointer}.mobile-toc ul{list-style:none;padding-left:12px}.mobile-toc li{margin:8px 0}
}
@media(max-width:767px){
  .reader-header{height:68px;padding:0 20px;gap:14px}.brand{font-size:16px;gap:9px}.brand-mark{width:27px;height:32px;font-size:11px}
  .brand small{font-size:8px;letter-spacing:1px}.header-actions{gap:12px;font-size:11px}.header-actions button{padding:5px 7px}
  .header-actions kbd{display:none}.header-actions .theme-toggle{display:none!important}
  .reader-layout{display:block;padding:0 25px}
  .chapter-nav{position:static;height:auto;padding:25px 0;border-bottom:1px solid var(--line)}
  .js .chapter-nav{display:none}.js .chapter-nav.open{display:block;position:fixed;inset:68px 0 0;z-index:3;background:var(--bg);height:calc(100dvh - 68px);padding:25px;overflow:auto}
  .chapter-nav .mobile-theme:not([hidden]){display:block;text-align:left;margin-bottom:8px}
  main{padding-top:29px}.reading-context{margin-bottom:30px}.prose,:lang(zh-CN) .prose{font-size:17px;line-height:1.95}
  .prose h1{font-size:34px}.prose h2{font-size:26px;margin-top:42px;padding-top:23px}.prose h3{font-size:18px}
  .chapter-heading{margin-bottom:30px;padding-bottom:25px}.prose pre{font-size:12px;padding:18px 14px}.prose blockquote{padding-left:18px;font-size:14px}
  .page-turn{gap:20px;font-size:12px}.search-dialog{top:4dvh;max-height:90dvh;padding:22px}
  .overview-heading h1{font-size:40px}.prose .lead{font-size:15px}.course-index strong{font-size:28px}
  .course-index a{font-size:11px;padding-right:8px}.course-index a+a{padding-left:13px}
}
@media(max-width:359px){.reader-header{padding:0 16px}.brand-mark{display:none}.reader-layout{padding:0 21px}.header-actions{gap:9px}.brand{font-size:15px}}
@media print{
 .reader-header,.chapter-nav,.page-toc,.page-turn,footer,.code-copy,.mobile-toc{display:none!important}
 .reader-layout{display:block;max-width:none}main{padding:0}.prose,:lang(zh-CN) .prose{font-size:11pt}
 .prose pre,.prose table{overflow:visible}.prose h2,.prose h3{break-after:avoid}body{background:white;color:black}
}
/* Teaching boxes preserve the book's four roles without loud background colors. */
.prose .teaching-box{margin:30px 0;padding:20px 24px;border:1px solid var(--line);border-left:3px solid var(--accent);background:var(--panel);min-width:0}
.prose .teaching-title{margin:0 0 16px;font-family:var(--sans);font-size:16px;font-weight:650;line-height:1.6;color:var(--accent)}
.prose .teaching-box>:last-child{margin-bottom:0}.prose .body-pitfall{border-left-style:double;border-left-width:5px}
.prose .diagram{margin:28px 0;padding:18px 0;border-block:1px solid var(--line)}
.diagram-view{overflow:auto;overscroll-behavior:contain}.diagram-view:empty{display:none}
.diagram-view svg{display:block;width:min(100%,var(--diagram-width));max-width:100%!important;height:auto;margin:auto}
.diagram-expanded .diagram-view{max-height:75vh}
.diagram-expanded .diagram-view svg{width:var(--diagram-width);max-width:none!important;margin:0}
.diagram-zoom{display:block;margin:0 0 14px auto;font:13px var(--sans);color:var(--accent);border:1px solid var(--line);background:var(--bg);padding:7px 12px;cursor:pointer}
.diagram-source{font:13px/1.7 var(--sans);color:var(--muted);margin-top:16px}.diagram-source summary{cursor:pointer}
@media(max-width:767px){.prose .teaching-box{padding:16px;margin:24px 0}.prose .teaching-title{font-size:15px}}
@media print{.diagram-zoom,.diagram-source{display:none}.diagram-view{max-height:none;overflow:visible}.diagram-expanded .diagram-view svg{width:100%;max-width:100%!important}}