옵셔널 타입

<div class="r2 option" data-step="0"><div class="r2-head">OPTION PATHS<span class="r2-live"></span></div><div class="r2-stage"><div class="r2-option-input">lookup(key)</div><div class="r2-option-paths"><div class="r2-option-some">Some(value)<small>use value</small></div><div class="r2-option-none">None<small>fallback</small></div></div></div><div class="r2-foot"><span class="r2-caption"></span><span class="r2-progress"></span></div></div>

.r2{width:min(95vw,730px);height:min(92vh,330px);padding:clamp(9px,2.5vmin,17px);display:flex;flex-direction:column;gap:7px;border:1px solid var(--line);border-radius:13px;background:var(--surface);color:var(--fg);font:500 clamp(12px,3.4vmin,16px)/1.25 var(--font-sans,sans-serif)}.r2 *{box-sizing:border-box}.r2-head{display:flex;justify-content:space-between;align-items:center;min-height:17px;color:var(--accent);font-size:12px;font-weight:700;letter-spacing:.03em}.r2-live{height:7px;width:7px;border-radius:50%;background:var(--accent);animation:r2beat 1.1s infinite}@keyframes r2beat{50%{opacity:.25}}.r2-stage{flex:1;min-height:0;position:relative;overflow:hidden}.r2-foot{min-height:27px;display:flex;align-items:center;justify-content:space-between;gap:8px;font-size:12px}.r2-caption{min-width:0}.r2-progress{flex:none;color:var(--accent);font:600 12px ui-monospace,monospace}.option .r2-stage{display:flex;flex-direction:column;align-items:center;justify-content:center;gap:12px}.r2-option-input{padding:7px 12px;border:1px solid var(--accent);border-radius:7px;background:var(--bg);font:600 12px ui-monospace,monospace}.r2-option-paths{width:min(100%,310px);display:flex;gap:8px}.r2-option-paths>div{flex:1;display:flex;flex-direction:column;align-items:center;gap:4px;padding:12px 3px;border:1px solid var(--line);border-radius:8px;background:var(--bg);font:600 12px ui-monospace,monospace;transition:opacity .3s,transform .3s,background .3s}.r2-option-paths small{font:500 12px var(--font-sans,sans-serif);color:var(--muted)}.option[data-step="0"] .r2-option-input,.option[data-step="1"] .r2-option-some,.option[data-step="2"] .r2-option-none{border-color:var(--accent);background:color-mix(in srgb,var(--accent) 14%,var(--surface));transform:translateY(-3px)}.option[data-step="1"] .r2-option-none,.option[data-step="2"] .r2-option-some{opacity:.35}

const root=document.querySelector('.r2'),caption=root.querySelector('.r2-caption'),progress=root.querySelector('.r2-progress'),labels=["Lookup returns an option","Some carries the value","None uses a fallback"];let step=0;function advance(){root.dataset.step=String(step);caption.textContent=labels[step];progress.textContent=(step+1)+' / '+labels.length;step=(step+1)%labels.length}advance();const timer=setInterval(advance,1000);root.addEventListener('pointerdown',()=>{clearInterval(timer);advance()})