/* Shared course identity. Geometry and surface roles live in their own sheets. */
:root {
  --navy:#002676;
  --gold:#fdb515;
  --ink:#182b43;
  --muted:#536377;
  --line:#dce1e7;
  --paper:#fff;
  --soft:#f0f4f8;
  --red:#a63138;
  --green:#176b60;
  --course-font:-apple-system,BlinkMacSystemFont,"PingFang SC","Microsoft YaHei",sans-serif;
}

/* Lecture03 spatial roles, adapted to Lecture04's proportional scene geometry. */
:root {
  --stage-gutter:16px; --stage-top:clamp(24px,3dvh,36px);
  --stage-gap:clamp(24px,3dvh,32px); --reading-measure:42em;
  font-family:var(--course-font);
  color:var(--ink); background:var(--paper);
}
*{box-sizing:border-box} body{margin:0}
button,a,input,select,textarea{-webkit-tap-highlight-color:transparent}
button,input,select,textarea{font:inherit} button,a{touch-action:manipulation}
button{border:1px solid var(--line);border-radius:4px;padding:10px 14px;background:var(--paper);color:var(--navy);cursor:pointer;min-height:44px}
button:hover{background:var(--soft)} button:disabled{opacity:.4;cursor:default}
a{color:var(--navy);text-underline-offset:.22em}
:is(button,a,input,select,textarea,summary):focus-visible{outline:3px solid var(--gold);outline-offset:3px}
::selection{background:#fdb51570}
button.primary{background:var(--navy);border-color:var(--navy);color:#fff} button.primary:hover{background:#18468e}
.sr-only{position:absolute;clip-path:inset(50%);width:1px;height:1px;overflow:hidden}
.skip{position:absolute;top:-100px}.skip:focus{top:10px;z-index:30;background:var(--paper);padding:12px}
[hidden]{display:none!important}
#main,dialog,#toast{display:none}.js #main{display:block}.js dialog[open]{display:grid}.js #toast:not(:empty){display:block}
.js:has(dialog[open]){overflow:hidden}

/* A clear title and breathing room precede a vertically balanced scene.
   Scene bounds discard unused paper rather than enlarging the side gutters. */
.classroom{position:relative;height:100dvh;display:grid;grid-template-rows:minmax(0,1fr) auto;margin:auto;min-width:0}
.canvas-page{min-height:0;min-width:0;display:grid;grid-template-rows:auto minmax(0,1fr);gap:var(--stage-gap);padding:var(--stage-top) var(--stage-gutter) 12px}
.page-heading{margin:0}.page-heading h1{font-size:clamp(40px,3.6vw,72px);line-height:1.16;letter-spacing:-.025em;color:var(--navy);font-weight:700;margin:0;text-wrap:pretty;overflow-wrap:break-word}
.scene-area{min-width:0;min-height:0;display:grid;grid-template-rows:minmax(0,1fr);position:relative}
.visual{position:relative;min-width:0;min-height:0;width:100%;display:flex;align-items:center;justify-content:center}
.visual>svg{display:block;width:100%;height:100%;font-family:inherit;flex:none}
.visual svg text{font-family:inherit}.visual svg image{isolation:isolate}
.scene-scroll-hint,.figure-link{display:none}
.cover-page{display:none}
.classroom[data-cover=true] .canvas-page{display:none}
.classroom[data-cover=true] .cover-page{display:grid;grid-template-rows:auto minmax(0,1fr) auto;gap:12px;padding:28px 32px 20px;background:#fafaf7;min-height:0}
.cover-heading h1{font-size:clamp(36px,3.4vw,60px);line-height:1.22;letter-spacing:-.025em;color:var(--navy);font-weight:650;margin:0}
.cover-heading p{font-size:clamp(20px,1.7vw,28px);line-height:1.5;color:var(--navy);margin:10px 0 0}
.cover-art{margin:0;min-width:0;min-height:0;display:flex;align-items:center;justify-content:center}
.cover-art img{display:block;width:100%;height:100%;object-fit:contain}
.cover-footer{display:flex;align-items:center;justify-content:space-between;gap:24px;font-size:22px;line-height:1.5;color:var(--navy)}
.cover-footer p{margin:0}.cover-footer a{color:inherit;text-underline-offset:5px;min-height:44px;display:flex;align-items:center}

/* One quiet dock. DOM and visual order stay the same at every width. */
.navigation{border-top:1px solid var(--line);display:grid;grid-template-columns:minmax(0,1fr) auto minmax(0,1fr);align-items:center;gap:16px;min-height:52px;padding:4px 24px calc(4px + env(safe-area-inset-bottom));background:var(--paper)}
.nav-group{display:flex;align-items:center;gap:8px;min-width:0}.nav-middle{justify-content:center}.nav-right{justify-content:flex-end}
.count,.beat-count{font-size:13px;color:var(--muted);font-variant-numeric:tabular-nums;white-space:nowrap}
.beat-count{margin-right:4px}.nav-group button{font-size:15px;border-color:transparent;padding:10px 12px;white-space:nowrap}
.nav-group button.primary{min-width:104px;border-color:var(--navy)}.nav-group button svg{width:20px;height:20px;display:block}
.nav-group .icon-button,.nav-group #previous{min-width:44px;padding:10px 12px}
.nav-group #open-guide{font-size:15px;padding:10px 6px;text-decoration:none;white-space:nowrap}
.questionnaire{font-size:15px;white-space:nowrap;text-decoration:none;padding:10px 8px}
.progress{height:3px;background:var(--soft);position:absolute;bottom:env(safe-area-inset-bottom);left:0;width:100%;pointer-events:none}.progress span{display:block;height:100%;background:var(--gold)}
#toast{position:fixed;bottom:78px;left:50%;transform:translateX(-50%);padding:10px 18px;background:var(--navy);color:#fff;border-radius:4px;z-index:30;font-size:16px}#toast:empty{display:none}

/* A stable heading and independently scrolling reading body. */
dialog{border:0;border-radius:8px;padding:0;box-shadow:0 18px 70px #10213b40;color:var(--ink);background:var(--paper);width:min(940px,calc(100vw - 48px));max-width:none;height:min(860px,calc(100dvh - 64px));max-height:none;grid-template-rows:auto minmax(0,1fr)}
dialog::backdrop{background:#10213b7a}
dialog>header{display:flex;justify-content:space-between;align-items:flex-start;gap:24px;padding:24px 32px 20px;border-bottom:1px solid var(--line)}
dialog>header h2{font-size:26px;line-height:1.4;font-weight:650;color:var(--navy);margin:0;min-width:0;text-wrap:pretty}
dialog>header button{flex:none;white-space:nowrap;font-size:15px}
.dialog-body{min-height:0;overflow:auto;overscroll-behavior:contain;scrollbar-color:var(--muted) var(--soft);padding:24px 36px 36px}
.dialog-body>.reading-body{max-width:var(--reading-measure);margin:auto}
dialog .fine{font-size:15px;color:var(--muted)} dialog details{padding:16px 0;border-top:1px solid var(--line)}
dialog summary{cursor:pointer;font-size:18px;line-height:1.7;color:var(--navy)}dialog iframe{width:100%;height:65vh;border:1px solid var(--line)}
.index-grid{display:block}.index-chapter{margin:0 0 20px}.index-chapter-links{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));column-gap:24px}
.index-grid a{padding:12px 4px;display:flex;align-items:baseline;gap:12px;text-decoration:none;border-bottom:1px solid var(--line);font-size:16px;line-height:1.5;min-height:44px}
.index-grid a:hover{background:var(--soft)}.index-grid a[aria-current=true]{background:#fff4d8}.index-grid span{font-variant-numeric:tabular-nums;color:var(--muted)}
.chapter-heading{color:var(--navy);font-size:21px;line-height:1.5;margin:24px 0 8px}.index-search{width:100%;padding:12px;border:1px solid var(--line);border-radius:4px;margin:0 0 12px;font-size:16px}
.index-status{font-size:15px;line-height:1.6;color:var(--muted);margin:0 0 16px}.index-grid .index-chapter:first-child .chapter-heading{margin-top:0}

/* Shared prose roles for notes, materials and the no-script reading fallback. */
.reading-body{font-size:18px;line-height:1.85;overflow-wrap:break-word}
.reading-body p,.reading-body li{font-size:1em;line-height:inherit}.reading-body p{margin:.8em 0 1em}
.reading-body h2{font-size:24px;line-height:1.45;color:var(--navy);margin:1.7em 0 .65em;font-weight:650;text-wrap:pretty}
.reading-body h3{font-size:21px;line-height:1.5;color:var(--navy);margin:1.4em 0 .5em;font-weight:650}
.reading-body strong{font-weight:650;color:var(--navy)}.reading-body blockquote{margin:1.5em 0;padding:0 1.2em;border-left:1px solid var(--line)}
.reading-body img{max-width:100%;height:auto;display:block;margin:1.2em auto}.reading-body pre{max-width:100%;overflow:auto;background:var(--soft);padding:18px;line-height:1.65}
.reading-body code{font-size:.9em}.reading-body a{overflow-wrap:anywhere}.reading-body .list-item{padding-left:1.1em;position:relative}.list-item::before{content:'·';position:absolute;left:0}
.reading-body .typeset-block{scroll-margin-top:24px}.reading-body .typeset-block:target{outline:1px solid var(--gold);outline-offset:4px}
.reading-nav{font-size:16px;display:flex;gap:12px 24px;flex-wrap:wrap;margin-bottom:24px}.reading-nav a{text-decoration:none}.reading-nav a:hover{text-decoration:underline}
.note-figure{margin:1.5em -16px 1.7em}.note-figure svg{display:block;width:100%;height:auto}.note-figure figcaption{font-size:15px;line-height:1.7;color:var(--muted);margin:8px 16px}
.current-beat{font-size:15px!important;color:var(--muted);padding-bottom:1em;border-bottom:1px solid var(--line)}.topic-anchor{display:block;scroll-margin-top:24px}
.note-actions{font-size:16px;display:flex;align-items:center;flex-wrap:wrap;gap:12px 24px;margin:16px 0;padding-bottom:18px;border-bottom:1px solid var(--line)}.note-actions button{font-size:15px}
.material{padding:0 0 24px;margin-bottom:24px;border-bottom:1px solid var(--line)}.material:last-child{border-bottom:0;margin-bottom:0}.material h3{margin-top:1em}
.material-links{display:flex;flex-wrap:wrap;gap:14px;margin:24px 0}.read-position{color:var(--muted);font-size:16px!important}
.adjacent-pages{display:flex;flex-direction:column;gap:12px;border-top:1px solid var(--line);padding-top:24px;margin-top:40px}
.continuous article{margin:64px 0;padding-top:28px;border-top:1px solid var(--line)}.continuous article>h2{margin-top:0}
.guide .lead{font-size:22px;line-height:1.7}.questionnaire-entry{padding:16px 0;border-bottom:1px solid var(--line)}.linked-topic{padding:0 0 18px;border-bottom:1px solid var(--line)}
.reading-links{font-size:16px!important;margin:2em 0!important}.legacy-trigger{font-size:14px;color:var(--red)}.visual-notes li{margin:.5em 0}.visual-notes li,.visual-notes p{white-space:pre-wrap;overflow-wrap:anywhere}
.semantic-page{max-width:1060px;margin:auto;padding:32px 28px 70px;line-height:1.75}.semantic-page.reading-body{max-width:880px}
.semantic-page h1{font-size:34px;line-height:1.35;color:var(--navy)}.semantic-page h2{color:var(--navy);margin-top:40px}.semantic-page h3{margin-top:26px}
.semantic-page p,.semantic-page li{font-size:18px}.semantic-page .frame{width:100%;border-bottom:1px solid var(--line);padding:18px 0}.semantic-page .frame svg{width:100%;height:auto}
.semantic-page details{border-top:1px solid var(--line);padding:14px 0}.semantic-page nav{display:flex;gap:18px;flex-wrap:wrap}.semantic-page pre{overflow:auto;background:var(--soft);padding:20px}
.semantic-page img{max-width:100%}.semantic-page table{border-collapse:collapse;width:100%}.semantic-page td,.semantic-page th{text-align:left;padding:10px;border-bottom:1px solid var(--line)}.semantic-page small{color:var(--muted)}
.semantic-page.figure-page{padding:24px;max-width:none}.figure-page h1{font-size:24px}.figure-window{overflow:auto;scrollbar-color:var(--muted) var(--soft)}.figure-window>svg{display:block;width:100%;height:auto;min-width:960px}

@media(max-width:1000px){.navigation{gap:8px;padding-inline:16px}.nav-group{gap:4px}.questionnaire{display:none}}
@media(max-width:760px){
 .classroom{height:auto;min-height:100dvh;grid-template-rows:minmax(0,1fr) auto}
 .canvas-page{padding:28px 20px 20px;min-height:calc(100dvh - 52px - env(safe-area-inset-bottom));gap:24px}
 .page-heading h1{font-size:34px;line-height:1.25}
 .scene-area{display:flex;flex-direction:column;gap:12px}.visual{overflow-x:auto;justify-content:flex-start;flex:1;align-items:center;scrollbar-width:thin;scrollbar-color:var(--muted) var(--soft)}
 .visual>svg{width:960px;height:auto;min-width:960px;aspect-ratio:var(--scene-ratio,1200/570)}
 .scene-scroll-hint{display:block;margin:0;font-size:14px;line-height:1.5;color:var(--muted)}.figure-link{display:inline-flex;align-items:center;min-height:44px;align-self:flex-start;font-size:16px;text-underline-offset:4px}
 .navigation{position:sticky;bottom:0;z-index:5;grid-template-columns:auto minmax(0,1fr) auto;gap:4px;padding-inline:8px}
 .nav-group{gap:0}.count,.beat-count,#open-guide,#fullscreen{display:none}.nav-group button{font-size:14px;padding-inline:8px}.nav-group button.primary{min-width:78px}.nav-group #previous{min-width:44px;padding-inline:10px}
 .classroom[data-cover=true] .cover-page{min-height:calc(100dvh - 52px - env(safe-area-inset-bottom));grid-template-rows:auto minmax(240px,1fr) auto;padding:28px 20px 20px;gap:20px}.cover-heading h1{font-size:36px}.cover-heading p{font-size:20px}.cover-art img{min-height:240px}.cover-footer{font-size:16px;flex-wrap:wrap;gap:8px}
 dialog{width:100%;height:100dvh;max-height:100dvh;border-radius:0;margin:0}dialog>header{padding:20px;gap:16px}dialog>header h2{font-size:24px}.dialog-body{padding:20px 24px 32px}.reading-body h2{font-size:22px}.reading-body h3{font-size:20px}
 .index-chapter-links{grid-template-columns:1fr}.semantic-page,.semantic-page.reading-body{padding:24px 20px}.semantic-page h1{font-size:28px}.note-figure{margin:1.3em -8px}.note-figure figcaption{margin:8px}.reading-nav{gap:10px 18px;font-size:15px}.guide .lead{font-size:20px}.figure-page{padding:20px 12px}.figure-page h1{font-size:23px}
}
@media(min-width:761px) and (max-height:650px){.canvas-page{--stage-top:20px;--stage-gap:20px;padding-bottom:8px}.page-heading h1{font-size:clamp(36px,3.6vw,56px)}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important}}