DOM tree

<div class="v"><header>HTML → DOM <span id="src">&lt;main&gt;</span></header><div class="stage tree"><div class="root">document</div><div class="branch" id="main">main<div class="children"><div id="h">h1</div><div id="p">p</div></div></div></div><div class="muted" id="note">Token 1 / 3</div></div>

.v{width:min(94vw,760px);height:min(88vh,320px);padding:clamp(9px,2.4vmin,18px);border:1px solid var(--line);border-radius:12px;background:var(--surface);font:500 clamp(12px,2.4vmin,16px)/1.3 var(--font-sans,system-ui,sans-serif);display:flex;flex-direction:column;gap:clamp(5px,1.4vmin,10px);overflow:hidden}.v header{display:flex;align-items:center;justify-content:space-between;gap:8px;color:var(--accent);font-weight:700}.v header span{color:var(--muted);font-weight:500}.v .stage{flex:1;min-height:0;position:relative}.v .muted{color:var(--muted)}.v .active{background:color-mix(in srgb,var(--accent) 18%,var(--surface));border-color:var(--accent)!important;color:var(--fg)}.v button{font:inherit;color:var(--fg);background:var(--bg);border:1px solid var(--line);border-radius:7px;padding:5px 8px;cursor:pointer}.tree{display:flex;align-items:center;justify-content:center;flex-direction:column;gap:5px}.root,.branch,.children div{border:1px solid var(--line);border-radius:7px;background:var(--bg);padding:5px 12px;text-align:center}.branch{position:relative;opacity:.25;transition:opacity .25s}.children{display:flex;gap:9px;margin-top:7px}.children div{opacity:.25;min-width:56px;transition:opacity .25s}.tree .on{opacity:1;border-color:var(--accent)}

let i=0;const names=["main","h","p"],tags=["<main>","<h1>","<p>"];function tick(){names.forEach((n,j)=>document.getElementById(n).classList.toggle("on",j<=i));document.getElementById("src").textContent=tags[i];document.getElementById("note").textContent="Token "+(i+1)+" / 3";i=(i+1)%3}tick();setInterval(tick,800)