#icosahedron-lesson{--ink:#2d3437;--muted:#616c6d;--line:#d4d9d5;--paper:#fff;--accent:#557b7c;--tint:#f7f9f8;box-sizing:border-box;max-width:1240px;margin:auto;padding:38px 40px 64px;font:16px/1.65 Arial,Helvetica,sans-serif;color:var(--ink);background:var(--paper);color-scheme:light;container-type:inline-size;container-name:collection-lesson}
#icosahedron-lesson *,#icosahedron-lesson *::before,#icosahedron-lesson *::after{box-sizing:border-box}
#icosahedron-lesson h1,#icosahedron-lesson h2,#icosahedron-lesson h3,#icosahedron-lesson p,#icosahedron-lesson figure,#icosahedron-lesson dl{margin:0}
#icosahedron-lesson h1{font:clamp(37px,4.5vw,60px)/1.1 Georgia,'Times New Roman',serif;letter-spacing:-.025em;font-weight:400;overflow-wrap:break-word}
#icosahedron-lesson h2{font:31px/1.2 Georgia,'Times New Roman',serif;font-weight:400;letter-spacing:-.01em;margin-bottom:15px}
#icosahedron-lesson h3{font-size:17px;line-height:1.35;margin-bottom:10px}
#icosahedron-lesson p+p{margin-top:13px}
#icosahedron-lesson button,#icosahedron-lesson input,#icosahedron-lesson select{font:inherit;color:inherit}
#icosahedron-lesson button,#icosahedron-lesson select,#icosahedron-lesson input[type=range]{cursor:pointer}
#icosahedron-lesson button{border:1px solid var(--line);border-radius:3px;background:#fff;padding:9px 13px;line-height:1.35;min-height:42px}
#icosahedron-lesson button:hover{background:var(--tint);border-color:var(--accent)}
#icosahedron-lesson button[aria-pressed=true]{background:var(--accent);border-color:var(--accent);color:#fff}
#icosahedron-lesson button:focus-visible,#icosahedron-lesson a:focus-visible,#icosahedron-lesson input:focus-visible,#icosahedron-lesson select:focus-visible{outline:3px solid var(--accent);outline-offset:3px}
#icosahedron-lesson [hidden]{display:none!important}
#icosahedron-lesson button:disabled,#icosahedron-lesson input:disabled,#icosahedron-lesson select:disabled{cursor:default;opacity:.6}
#icosahedron-lesson button:disabled{pointer-events:none}
#icosahedron-lesson .opening{margin-bottom:24px}
#icosahedron-lesson .deck{font:24px/1.35 Georgia,serif;color:var(--accent);margin-top:14px}
#icosahedron-lesson .definition{margin-top:15px;line-height:1.75}
#icosahedron-lesson .chapter-nav{display:flex;gap:7px 24px;flex-wrap:wrap;border-block:1px solid var(--line);padding:11px 0;margin:25px 0}
#icosahedron-lesson .chapter-nav a{color:var(--ink);text-decoration:none;font-size:14px;padding:3px 0;border-bottom:2px solid transparent}
#icosahedron-lesson .chapter-nav a:hover{border-bottom-color:var(--accent)}
#icosahedron-lesson .model-panel{border:1px solid var(--line);background:var(--tint);min-width:0;position:relative}
#icosahedron-lesson .model-toolbar{display:flex;align-items:flex-start;justify-content:space-between;gap:10px;padding:13px 14px;border-bottom:1px solid var(--line);background:#fff}
#icosahedron-lesson .mode-tabs{display:flex;flex-wrap:wrap;gap:5px}
#icosahedron-lesson .mode-tabs button{font-size:13px;padding:8px 10px;min-height:36px}
#icosahedron-lesson .fullscreen{white-space:nowrap;font-size:13px;min-height:36px;padding:8px}
#icosahedron-lesson .model-stage{height:490px;position:relative;overflow:hidden;touch-action:none;outline-offset:-4px}
#icosahedron-lesson .model-stage canvas{position:absolute;inset:0;display:block;width:100%;height:100%;touch-action:none}
#icosahedron-lesson .model-stage>svg{position:absolute;inset:0;pointer-events:none;width:100%;height:100%}
#icosahedron-lesson .model-stage text{font:600 13px Arial,sans-serif;paint-order:stroke;stroke:var(--tint);stroke-width:5px;stroke-linejoin:round}
#icosahedron-lesson .model-fallback{position:absolute;inset:0;display:flex;flex-direction:column;align-items:center;justify-content:center}
#icosahedron-lesson .model-fallback img{display:block;object-fit:contain;width:100%;height:calc(100% - 45px)}
#icosahedron-lesson .model-fallback p{font-size:13px;text-align:center;padding:5px}
#icosahedron-lesson .camera-controls{display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap;padding:10px 14px;background:rgba(255,255,255,.8)}
#icosahedron-lesson .camera-controls p{font-size:12px;color:var(--muted)}
#icosahedron-lesson .camera-controls>div{display:flex;gap:4px}
#icosahedron-lesson .camera-controls button{font-size:12px;padding:6px 9px;min-height:34px}
#icosahedron-lesson .model-status{font-size:12px;color:var(--muted);padding:9px 14px;border-top:1px solid var(--line);min-height:38px}
#icosahedron-lesson .view-adjustment{padding:12px 18px;display:flex;align-items:center;gap:18px;flex-wrap:wrap;border-top:1px solid var(--line);font-size:13px}
#icosahedron-lesson .view-adjustment input{flex:1;min-width:130px;accent-color:var(--accent)}
#icosahedron-lesson .view-adjustment span{font-variant-numeric:tabular-nums}
#icosahedron-lesson .dimensions{min-width:0}
#icosahedron-lesson .dimension{margin-bottom:18px}
#icosahedron-lesson .dimension label{display:block;font-size:14px;font-weight:600;margin-bottom:7px}
#icosahedron-lesson .dimension>div{display:flex;align-items:center;gap:15px}
#icosahedron-lesson .dimension input[type=number]{width:85px;min-width:0;border:1px solid #adb8b6;background:#fff;padding:8px;font:20px Georgia,serif;border-radius:2px}
#icosahedron-lesson .dimension input[type=range]{min-width:30px;flex:1;accent-color:var(--accent);height:30px}
#icosahedron-lesson .units-row{display:flex;align-items:center;gap:12px;font-size:13px;margin-top:20px}
#icosahedron-lesson .units-row select{padding:7px 23px 7px 8px;border:1px solid var(--line);background:#fff;border-radius:2px;max-width:100%}
#icosahedron-lesson .fine-print{font-size:12px;line-height:1.6;color:var(--muted);margin-top:13px}
#icosahedron-lesson .input-error{font-size:13px;color:#962d29;margin:12px 0}
#icosahedron-lesson .answer{min-width:0;padding:15px 0;border-bottom:1px solid var(--line)}
#icosahedron-lesson .answer>span{font-size:13px;font-weight:600;letter-spacing:.01em}
#icosahedron-lesson .answer p{font:32px/1.2 Georgia,serif;font-variant-numeric:tabular-nums;margin-top:7px;overflow-wrap:anywhere;color:var(--ink)}
#icosahedron-lesson .answer .unit{font:13px Arial,sans-serif;color:var(--muted);white-space:nowrap}
#icosahedron-lesson .answer small{display:block;font:12px/1.5 Arial,sans-serif;color:var(--muted);margin-top:8px}
#icosahedron-lesson .result-pair{display:grid;grid-template-columns:1fr 1fr;gap:25px}
#icosahedron-lesson .result-pair .answer{padding:20px 24px;background:var(--tint);border-left:3px solid var(--accent);border-bottom:0}
#icosahedron-lesson .tally{display:flex;gap:28px;margin:14px 0}
#icosahedron-lesson .tally>div{display:flex;flex-direction:column-reverse}
#icosahedron-lesson .tally dt{font-size:12px;color:var(--muted)}
#icosahedron-lesson .tally dd{margin:0;font:31px/1.2 Georgia,serif}
#icosahedron-lesson .topology-note{font-size:13px;color:var(--muted);padding:12px 0}
#icosahedron-lesson .face-select{display:flex;flex-wrap:wrap;align-items:center;gap:10px;font-size:13px;padding:14px 0}
#icosahedron-lesson .face-select select{padding:7px;border:1px solid var(--line);background:#fff;max-width:100%}
#icosahedron-lesson .families{display:flex;flex-wrap:wrap;gap:7px;margin:13px 0}
#icosahedron-lesson .families button{font-size:13px}
#icosahedron-lesson .table-wrap{overflow:auto;margin:22px 0;max-width:100%}
#icosahedron-lesson table{width:100%;border-collapse:collapse;text-align:left;font-size:14px;min-width:520px}
#icosahedron-lesson caption{text-align:left;font:22px Georgia,serif;padding:0 0 17px}
#icosahedron-lesson th,#icosahedron-lesson td{padding:13px 15px;border-bottom:1px solid var(--line);vertical-align:top}
#icosahedron-lesson thead{background:var(--tint)}
#icosahedron-lesson tbody th{font-weight:400}
#icosahedron-lesson td .unit{white-space:nowrap;font-size:11px;color:var(--muted)}
#icosahedron-lesson .formula{font-family:Georgia,serif;white-space:nowrap}
#icosahedron-lesson .featured-section{margin:48px 0;border-top:1px solid var(--line);padding-top:29px}
#icosahedron-lesson .featured-variants{border:1px solid var(--line);background:var(--tint)}
#icosahedron-lesson .featured-variants img{display:block;width:100%;height:auto}
#icosahedron-lesson .featured-variants .featured-mobile{display:none}
#icosahedron-lesson figcaption{font-size:12px;color:var(--muted);line-height:1.6;padding:12px 0}
#icosahedron-lesson .study-diagram img{display:block;width:100%;height:auto}
#icosahedron-lesson .study-diagram{min-width:0}
#icosahedron-lesson .questions{margin-top:40px;max-width:none}
#icosahedron-lesson details{border-top:1px solid var(--line);padding:15px 0}
#icosahedron-lesson summary{cursor:pointer;font-size:15px;font-weight:600;line-height:1.5;padding-right:15px}
#icosahedron-lesson details p{font-size:14px;max-width:none;margin:12px 0 3px}
#icosahedron-lesson .text-action{color:var(--accent);border:0;border-bottom:1px solid var(--accent);border-radius:0;background:transparent;padding:8px 0;font-size:14px;margin-top:13px;text-align:left}
#icosahedron-lesson .text-action:hover{background:transparent}
#icosahedron-lesson .text-action span{margin-left:8px}
#icosahedron-lesson .study{margin:40px 0;border-top:1px solid var(--line);padding-top:30px}
#icosahedron-lesson .study p{max-width:none}
#icosahedron-lesson .formula-line{font:28px/1.5 Georgia,serif;color:var(--accent);margin:18px 0}
#icosahedron-lesson .presets{display:flex;flex-wrap:wrap;gap:6px;margin:15px 0}
#icosahedron-lesson .presets button{font-size:13px}
#icosahedron-lesson .no-script{padding:18px;border:1px solid var(--line);margin-top:25px}
#icosahedron-lesson .model-dialog{padding:0;border:1px solid var(--line);width:calc(100vw - 30px);height:calc(100dvh - 30px);max-width:1600px;max-height:none;background:#fff;color:var(--ink)}
#icosahedron-lesson .model-dialog::backdrop{background:rgba(24,31,35,.65)}
#icosahedron-lesson .model-dialog .model-panel{height:100%;display:flex;flex-direction:column;border:0}
#icosahedron-lesson .model-dialog .model-stage{height:auto;min-height:180px;flex:1}
#icosahedron-lesson .model-panel:fullscreen{width:100vw;height:100dvh;display:flex;flex-direction:column}
#icosahedron-lesson .model-panel:fullscreen .model-stage{height:auto;flex:1;min-height:180px}
@media(max-width:850px){#icosahedron-lesson{padding:27px 24px 45px}#icosahedron-lesson .model-stage{height:430px}#icosahedron-lesson h1{font-size:43px}#icosahedron-lesson .result-pair{gap:15px}#icosahedron-lesson .answer p{font-size:29px}}
@media(max-width:600px){#icosahedron-lesson{padding:23px 17px 40px}#icosahedron-lesson h1{font-size:36px}#icosahedron-lesson h2{font-size:27px}#icosahedron-lesson .deck{font-size:21px}#icosahedron-lesson .definition{font-size:15px}#icosahedron-lesson .chapter-nav{gap:7px;border:0;background:var(--tint);padding:9px;border-radius:3px;display:grid;grid-template-columns:1fr 1fr}#icosahedron-lesson .chapter-nav a{border:1px solid var(--line);padding:9px 10px;background:#fff;font-size:12px;border-radius:2px}#icosahedron-lesson .model-stage{height:370px}#icosahedron-lesson .model-toolbar{padding:10px;gap:5px;flex-wrap:wrap}#icosahedron-lesson .mode-tabs{flex:1}#icosahedron-lesson .mode-tabs button{font-size:12px}#icosahedron-lesson .camera-controls{justify-content:center;padding:9px}#icosahedron-lesson .camera-controls p{width:100%;text-align:center}#icosahedron-lesson .view-adjustment{gap:8px;padding:12px}#icosahedron-lesson .view-adjustment label{width:100%}#icosahedron-lesson .result-pair{grid-template-columns:1fr;gap:10px}#icosahedron-lesson .result-pair .answer{padding:16px 18px}#icosahedron-lesson .featured-variants .featured-desktop{display:none}#icosahedron-lesson .featured-variants .featured-mobile{display:block}#icosahedron-lesson .featured-section{margin:32px 0}#icosahedron-lesson .tally{justify-content:space-between;margin:20px 0}#icosahedron-lesson .model-dialog{width:100vw;height:100dvh;margin:0}#icosahedron-lesson .model-dialog .model-toolbar{padding:8px}#icosahedron-lesson .table-wrap{margin-right:-4px;width:calc(100% + 4px)}#icosahedron-lesson th,#icosahedron-lesson td{padding:12px 10px}#icosahedron-lesson .study{margin:30px 0}}
@media(prefers-reduced-motion:reduce){#icosahedron-lesson *{scroll-behavior:auto!important}}

#icosahedron-lesson .ico-workshop{display:grid;grid-template-columns:minmax(0,1fr) 280px;gap:30px}#icosahedron-lesson .ico-ledger{border-left:1px solid var(--line);padding-left:28px}#icosahedron-lesson .ico-ledger h2{font-size:27px}#icosahedron-lesson .ico-ledger .tally{gap:23px}#icosahedron-lesson .ico-ledger .answer p{font-size:34px}#icosahedron-lesson .ico-triangles{display:grid;grid-template-columns:1.3fr 1fr;gap:60px}#icosahedron-lesson .ico-face-area{padding:25px 32px;background:var(--tint)}#icosahedron-lesson .ico-face-area>strong{display:block;font:42px Georgia,serif;margin:13px 0}#icosahedron-lesson .ico-face-area>span{font-size:13px}#icosahedron-lesson .ico-face-area>p{font-size:14px}@media(max-width:850px){#icosahedron-lesson .ico-workshop{grid-template-columns:1fr}#icosahedron-lesson .ico-ledger{border-left:0;padding:20px;border-top:3px solid var(--accent);display:grid;grid-template-columns:1fr 1fr;gap:10px 25px}#icosahedron-lesson .ico-ledger h2{grid-column:1/-1}#icosahedron-lesson .ico-ledger .tally{align-items:center}#icosahedron-lesson .ico-triangles{gap:25px}}@media(max-width:600px){#icosahedron-lesson .ico-ledger,#icosahedron-lesson .ico-triangles{display:block}#icosahedron-lesson .ico-ledger{padding:18px}#icosahedron-lesson .ico-face-area{margin-top:20px}}/* Search-intent composition */

/* Topic studies: shared reading primitives; each composition is authored below. */
#icosahedron-lesson .search-study{margin:40px 0;padding:30px 0;border-block:1px solid var(--line);min-width:0}
#icosahedron-lesson .search-study p{max-width:none}
#icosahedron-lesson .search-study h2{margin-bottom:16px}
#icosahedron-lesson .search-study h3{margin:0 0 10px}
#icosahedron-lesson .search-study figure{margin:0;min-width:0}
#icosahedron-lesson .search-net img{display:block;width:100%;height:auto;background:#fdfcf8;border:1px solid var(--line)}
#icosahedron-lesson .search-net figcaption{font-size:12px;line-height:1.65;color:var(--muted);padding:10px 0}
#icosahedron-lesson .search-study .text-action{margin-top:14px;margin-right:9px;white-space:normal;text-align:left}
#icosahedron-lesson .study-split{display:grid;grid-template-columns:1fr 1fr;gap:30px;align-items:start;margin-top:22px}
#icosahedron-lesson .study-foot{display:flex;gap:30px;align-items:center;justify-content:space-between;margin-top:20px}
#icosahedron-lesson .study-foot>p,#icosahedron-lesson .study-foot>div{flex:1}
#icosahedron-lesson .study-note{padding:20px;background:var(--tint);border-left:3px solid var(--accent);margin-top:20px}
#icosahedron-lesson .study-equation-row{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:20px;margin:22px 0}
#icosahedron-lesson .study-equation-row>div,#icosahedron-lesson .study-equation-row>p{margin:0;padding:18px 20px;background:var(--tint);border-top:2px solid var(--accent)}
#icosahedron-lesson .study-ledger{margin:20px 0}
#icosahedron-lesson .study-ledger>div{display:flex;justify-content:space-between;gap:20px;padding:12px 0;border-bottom:1px solid var(--line)}
#icosahedron-lesson .study-ledger dd{margin:0;font-variant-numeric:tabular-nums;text-align:right}
#icosahedron-lesson .study-counts{display:flex;gap:20px;flex-wrap:wrap;margin:22px 0 12px}
#icosahedron-lesson .study-counts b{font:30px Georgia,serif;margin-right:5px}
#icosahedron-lesson .study-large-equation{font:clamp(20px,3vw,29px)/1.7 Georgia,serif;background:var(--tint);padding:22px;overflow-wrap:anywhere}
#icosahedron-lesson .point-form>div{display:flex;gap:14px;margin:15px 0}
#icosahedron-lesson .point-form label{flex:1;min-width:0}
#icosahedron-lesson .point-form input{display:block;width:100%;min-height:44px;border:1px solid var(--line);padding:8px}
#icosahedron-lesson .point-form [role=status]{margin-top:15px}
@container collection-lesson (max-width:700px){#icosahedron-lesson .search-study .study-split,#icosahedron-lesson .search-study .study-equation-row{grid-template-columns:1fr}#icosahedron-lesson .search-study .study-foot{display:block}#icosahedron-lesson .study-ledger>div{flex-wrap:wrap}#icosahedron-lesson .study-ledger dd{text-align:left}}
#icosahedron-lesson .ico-net-map{display:grid;grid-template-columns:.85fr 1.15fr;gap:30px;align-items:center}
@container collection-lesson (max-width:760px){#icosahedron-lesson .search-study{display:block}#icosahedron-lesson .search-study>.search-net{margin:22px 0}#icosahedron-lesson .search-study .study-heading{display:block}#icosahedron-lesson .search-study .study-split{grid-template-columns:1fr}}

#icosahedron-lesson{--accent:#3c777b;--tint:#f7faf9;}
/* Shared reading and navigation behavior; each lesson keeps its composition. */
#icosahedron-lesson .mobile-contents { display: none; }
#icosahedron-lesson .mobile-contents summary { list-style: none; }
#icosahedron-lesson .mobile-contents summary::-webkit-details-marker { display: none; }

@media (max-width: 760px) {
  #icosahedron-lesson [data-desktop-contents] { display: none !important; }
  #icosahedron-lesson .mobile-contents { display: block; }
}
@container collection-lesson (max-width: 760px) {
  #icosahedron-lesson [data-desktop-contents] { display: none !important; }
  #icosahedron-lesson .mobile-contents { display: block; }
}
#icosahedron-lesson .mobile-contents {
  margin: 20px 0 24px;
  padding: 0;
  max-width: none;
  border: 1px solid var(--line, #ccd6dc);
  border-radius: 3px;
  background: #fff;
  color: var(--ink, #294e69);
  font: 15px/1.45 Arial, Helvetica, sans-serif;
}
#icosahedron-lesson .mobile-contents > summary {
  display: flex;
  align-items: center;
  gap: 12px;
  min-height: 56px;
  padding: 12px 16px;
  cursor: pointer;
  background: var(--tint, var(--paper, #f4f7f9));
  color: inherit;
}
#icosahedron-lesson .mobile-contents .contents-title { font-weight: 700; }
#icosahedron-lesson .mobile-contents .contents-count {
  margin-left: auto;
  font-size: 12px;
  font-weight: 400;
  color: var(--muted, #617582);
  white-space: nowrap;
}
#icosahedron-lesson .mobile-contents > summary::after {
  content: '';
  width: 7px;
  height: 7px;
  flex: none;
  margin-left: 3px;
  border-right: 1.5px solid currentColor;
  border-bottom: 1.5px solid currentColor;
  transform: translateY(-2px) rotate(45deg);
}
#icosahedron-lesson .mobile-contents[open] > summary { border-bottom: 1px solid var(--line, #ccd6dc); }
#icosahedron-lesson .mobile-contents[open] > summary::after { transform: translateY(2px) rotate(225deg); }
#icosahedron-lesson .mobile-contents nav { display: block; padding: 0 16px; margin: 0; border: 0; }
#icosahedron-lesson .mobile-contents ol { list-style: none; padding: 0; margin: 0; }
#icosahedron-lesson .mobile-contents li { padding: 0; margin: 0; border-bottom: 1px solid var(--line, #dce3e7); }
#icosahedron-lesson .mobile-contents li:last-child { border-bottom: 0; }
#icosahedron-lesson .mobile-contents a {
  display: grid;
  grid-template-columns: 22px minmax(0, 1fr) 18px;
  align-items: center;
  gap: 10px;
  min-height: 50px;
  padding: 11px 0;
  color: inherit;
  font-size: 14px;
  line-height: 1.45;
  text-decoration: none;
  overflow-wrap: break-word;
}
#icosahedron-lesson .mobile-contents .contents-number { font-size: 11px; color: var(--muted, #617582); font-variant-numeric: tabular-nums; }
#icosahedron-lesson .mobile-contents .contents-arrow { color: var(--accent, var(--green, #315f81)); }
#icosahedron-lesson .mobile-contents a:hover { color: var(--accent, var(--green, #315f81)); text-decoration: underline; text-underline-offset: 3px; }
#icosahedron-lesson .mobile-contents a:focus-visible, #icosahedron-lesson .mobile-contents summary:focus-visible { outline: 2px solid var(--accent, var(--green, #315f81)); outline-offset: -3px; }

/* Keep the mode labels readable and separate them from the full-screen action. */
@media (max-width: 760px) {
  #icosahedron-lesson .model-toolbar, #icosahedron-lesson .viewer-bar { flex-wrap: wrap; gap: 10px; }
  #icosahedron-lesson .mode-tabs, #icosahedron-lesson .mode-buttons { flex: 1 0 100%; display: flex; flex-wrap: wrap; gap: 6px; }
  #icosahedron-lesson .mode-tabs button, #icosahedron-lesson .mode-buttons button { flex: 1 1 auto; min-height: 44px; padding: 9px 12px; font-size: 13px; white-space: normal; }
  #icosahedron-lesson .model-toolbar .fullscreen, #icosahedron-lesson .viewer-bar .fullscreen { margin-left: auto; min-height: 44px; padding: 9px 12px; font-size: 13px; }
  #icosahedron-lesson .viewer-bar .fullscreen span { display: inline; }
  #icosahedron-lesson .camera-controls button { min-width: 44px; min-height: 44px; font-size: 13px; }
  #icosahedron-lesson .stage-top .view-switch { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); width: 100%; gap: 5px; border: 0; background: transparent; }
  #icosahedron-lesson .stage-top .view-switch button { min-height: 44px; padding: 9px 8px; font-size: 13px; border: 1px solid var(--line, #ccd6dc); background: #fff; white-space: normal; }
  #icosahedron-lesson .stage-top .view-switch button[aria-pressed=true] { background: var(--green, #315f81); color: #fff; }
  #icosahedron-lesson .stage > .viewport { top: 112px; }
  #icosahedron-lesson .stage { min-height: 480px; }
  #icosahedron-lesson .camera-buttons button, #icosahedron-lesson .camera-bar button { min-width: 44px; min-height: 44px; }
}
@container collection-lesson (max-width: 760px) {
  #icosahedron-lesson .model-toolbar, #icosahedron-lesson .viewer-bar { flex-wrap: wrap; gap: 10px; }
  #icosahedron-lesson .mode-tabs, #icosahedron-lesson .mode-buttons { flex: 1 0 100%; display: flex; flex-wrap: wrap; gap: 6px; }
  #icosahedron-lesson .mode-tabs button, #icosahedron-lesson .mode-buttons button { flex: 1 1 auto; min-height: 44px; padding: 9px 12px; font-size: 13px; white-space: normal; }
  #icosahedron-lesson .model-toolbar .fullscreen, #icosahedron-lesson .viewer-bar .fullscreen { margin-left: auto; min-height: 44px; padding: 9px 12px; font-size: 13px; }
  #icosahedron-lesson .viewer-bar .fullscreen span { display: inline; }
  #icosahedron-lesson .camera-controls button { min-width: 44px; min-height: 44px; font-size: 13px; }
  #icosahedron-lesson .stage-top .view-switch { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); width: 100%; gap: 5px; border: 0; background: transparent; }
  #icosahedron-lesson .stage-top .view-switch button { min-height: 44px; padding: 9px 8px; font-size: 13px; border: 1px solid var(--line, #ccd6dc); background: #fff; white-space: normal; }
  #icosahedron-lesson .stage-top .view-switch button[aria-pressed=true] { background: var(--green, #315f81); color: #fff; }
  #icosahedron-lesson .stage > .viewport { top: 112px; }
  #icosahedron-lesson .stage { min-height: 480px; }
  #icosahedron-lesson .camera-buttons button, #icosahedron-lesson .camera-bar button { min-width: 44px; min-height: 44px; }
}
#icosahedron-lesson .featured-pin {
  --pin-ink: #223b48;
  --pin-muted: #536672;
  --pin-rule: #cbd3d4;
  margin-top: 56px;
  color: var(--pin-ink);
  container-type: inline-size;
  container-name: pin-reference;
}
#icosahedron-lesson .featured-pin * { box-sizing: border-box; }
#icosahedron-lesson .featured-pin h2 { margin: 0; font: 42px/1.12 Georgia, serif; letter-spacing: -1.1px; color: inherit; }
#icosahedron-lesson .featured-pin h3 { margin: 0; color: inherit; }
#icosahedron-lesson .featured-pin p { margin: 0; max-width: none; }
#icosahedron-lesson .featured-pin .pin-intro { margin: 18px 0 26px; font-size: 15px; line-height: 1.75; color: var(--pin-muted); }
#icosahedron-lesson .featured-pin .pin-art { width: 100%; max-width: 420px; margin: 0; justify-self: center; min-width: 0; }
#icosahedron-lesson .featured-pin .pin-preview { display: block; line-height: 0; background: #fff; box-shadow: 0 8px 24px #132e3914; }
#icosahedron-lesson .featured-pin .pin-preview img { display: block; width: 100%; max-width: 100%; height: auto; aspect-ratio: 2 / 3; border: 1px solid #17344326; }
#icosahedron-lesson .featured-pin .pin-preview:hover { outline: 2px solid var(--pin-ink); outline-offset: 4px; }
#icosahedron-lesson .featured-pin figcaption { margin: 14px 0 0; padding: 0; text-align: center; font: 12px/1.5 Arial, sans-serif; color: var(--pin-muted); }
#icosahedron-lesson .featured-pin .pin-actions { display: flex; flex-wrap: wrap; align-items: stretch; gap: 10px; margin-top: 26px; }
#icosahedron-lesson .featured-pin .pin-actions :is(a, button) { display: inline-flex; justify-content: center; align-items: center; gap: 10px; min-height: 46px; padding: 10px 18px; font: 600 14px/1.4 Arial, sans-serif; text-decoration: none; border: 1px solid var(--pin-ink); border-radius: 0; cursor: pointer; }
#icosahedron-lesson .featured-pin .pin-actions .pin-pinterest { flex: 0 0 auto; padding-inline: 14px; background: #bd081b; border-color: #bd081b; color: #fff; }
#icosahedron-lesson .featured-pin .pin-actions .pin-pinterest:hover { background: #9b0716; border-color: #9b0716; }
#icosahedron-lesson .featured-pin .pin-save { background: transparent; color: var(--pin-ink); }
#icosahedron-lesson .featured-pin .pin-enlarge { background: transparent; color: var(--pin-ink); }
#icosahedron-lesson .featured-pin .pin-actions a:hover { text-decoration: underline; text-underline-offset: 4px; }
#icosahedron-lesson .featured-pin :is(a, button):focus-visible { outline: 3px solid var(--pin-ink); outline-offset: 4px; }
#icosahedron-lesson .featured-pin .pin-actions svg { width: 18px; height: 18px; fill: none; stroke: currentColor; stroke-width: 1.6; }
#icosahedron-lesson .featured-pin .pin-return { display: inline-flex; align-items: center; gap: 10px; min-height: 44px; margin-top: 16px; font-size: 13px; color: var(--pin-ink); text-underline-offset: 4px; }
#icosahedron-lesson .featured-pin .pin-sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; }
@container pin-reference (max-width: 700px) {
  #icosahedron-lesson .featured-pin h2 { font-size: 34px; letter-spacing: -.7px; }
  #icosahedron-lesson .featured-pin .pin-art { max-width: 420px; }
  #icosahedron-lesson .featured-pin .pin-intro { font-size: 15px; margin: 15px 0 22px; }
}
@media (max-width: 600px) {
  #icosahedron-lesson .featured-pin { margin-top: 36px; }
}

#icosahedron-lesson .featured-pin { --pin-ink: #244f4e; --pin-muted: #596773; --pin-rule: #ccd4d4; }
#icosahedron-lesson .topic-pin-icosahedron { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); grid-template-rows: auto 1fr; gap: 0 48px; border-top: 3px solid #244f4e; padding: 34px 28px; background: #edf4f2; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-heading { grid-column: 2; grid-row: 1; }
#icosahedron-lesson .topic-pin-icosahedron .pin-art { grid-column: 1; grid-row: 1 / 3; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-details { grid-column: 2; grid-row: 2; align-self: start; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-facts { margin: 0; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-facts > div { padding: 18px 0; border-top: 1px solid var(--pin-rule); }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-facts dt { font: 22px/1.3 Georgia, serif; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-facts dd { margin: 8px 0 0; color: var(--pin-muted); font-size: 14px; line-height: 1.7; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-heading { grid-column: 1 / -1; grid-row: 1; display: grid; grid-template-columns: 1fr 1fr; gap: 32px; align-items: end; padding-bottom: 24px; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-heading .pin-intro { margin-bottom: 0; }
#icosahedron-lesson .topic-pin-icosahedron .pin-art { grid-column: 1; grid-row: 2; }
#icosahedron-lesson .topic-pin-icosahedron .topic-pin-details { grid-column: 2; grid-row: 2; align-self: center; }
@container pin-reference (max-width: 850px) { #icosahedron-lesson .topic-pin-icosahedron { padding: 28px 20px; column-gap: 28px; } #icosahedron-lesson .topic-pin-icosahedron h2 { font-size: 34px; } }
@container pin-reference (max-width: 700px) {
  #icosahedron-lesson .topic-pin-icosahedron { grid-template-columns: minmax(0, 1fr); padding: 25px 18px; gap: 0; }
  #icosahedron-lesson .topic-pin-icosahedron .topic-pin-heading { grid-column: 1; grid-row: 1; display: block; text-align: left; padding-bottom: 0; }
  #icosahedron-lesson .topic-pin-icosahedron .topic-pin-heading .pin-intro { margin-bottom: 22px; }
  #icosahedron-lesson .topic-pin-icosahedron .pin-art { grid-column: 1; grid-row: 2; margin: 0 0 26px; }
  #icosahedron-lesson .topic-pin-icosahedron .topic-pin-details { grid-column: 1; grid-row: 3; }
}