Server-side rendering

<div class="demo"><div class="head"><strong>FIRST CONTENT</strong><span id="phase">request</span></div><div class="scene"><div class="row"><b>SSR</b><div class="track"><i id="ssr"></i></div><span id="ssrlabel">waiting</span></div><div class="row"><b>CSR</b><div class="track"><i id="csr"></i></div><span id="csrlabel">waiting</span></div></div><div class="foot"><span>HTML → JavaScript → interactive</span><span>tap to step</span></div></div>

.demo{width:min(92vw,660px);height:min(86vh,310px);border:1px solid var(--line);border-radius:14px;background:var(--surface);padding:clamp(10px,2.5vmin,20px);display:flex;flex-direction:column;gap:clamp(6px,1.7vmin,12px);box-shadow:0 10px 35px rgba(0,0,0,.07);font:500 clamp(10px,2.8vmin,15px)/1.35 ui-monospace,SFMono-Regular,Consolas,monospace}
.head,.foot{display:flex;align-items:center;justify-content:space-between;gap:8px}.head strong{color:var(--accent);font-size:1.05em}.foot{color:var(--muted);font-size:.85em;min-height:1.4em}.scene{flex:1;min-height:0;position:relative;display:flex;align-items:center;justify-content:center;gap:clamp(5px,1.5vmin,12px)}.chip{border:1px solid var(--line);background:var(--bg);border-radius:7px;padding:.4em .6em;text-align:center}.on{border-color:var(--accent)!important;background:color-mix(in srgb,var(--accent) 12%,var(--surface))!important;color:var(--accent)!important}.dim{opacity:.42}.arrow{color:var(--muted)}
.scene{flex-direction:column;align-items:stretch;justify-content:center}.row{display:flex;align-items:center;gap:8px;height:31%;min-height:32px}.row b{width:3em}.row span{width:6em;text-align:right}.track{flex:1;height:45%;border-radius:99px;background:var(--line);overflow:hidden}.track i{display:block;width:0;height:100%;background:var(--accent);transition:width .4s}

let step=0;const phases=["request","HTML arrives","JS runs","interactive"];function advance(){document.getElementById("phase").textContent=phases[step];document.getElementById("ssr").style.width=["0%","65%","85%","100%"][step];document.getElementById("csr").style.width=["0%","20%","65%","100%"][step];document.getElementById("ssrlabel").textContent=step>=1?"content":"waiting";document.getElementById("csrlabel").textContent=step>=2?"content":"waiting";step=(step+1)%4}advance();const timer=setInterval(advance,850);document.querySelector(".demo").addEventListener("pointerdown",()=>{clearInterval(timer);advance()})