Add three playable puzzle variants in an isolated lab

labs/variants/style.css

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+:root{font-family:system-ui,-apple-system,"PingFang SC",sans-serif;color:#253b4a;background:#eaf0f3;font-synthesis:none}*{box-sizing:border-box}body{margin:0}main{max-width:640px;margin:auto;padding:24px 20px}header,.level-row{display:flex;align-items:center;justify-content:space-between;gap:12px}header{font-size:12px;color:#657986}a{color:inherit}h1{font-size:27px;margin:30px 0 8px;letter-spacing:-1px}.intro{color:#657986;margin:0 0 24px;font-size:14px}button,select{font:inherit;border:1px solid #cbd7dd;border-radius:12px;background:#fff;color:#253b4a;padding:12px;cursor:pointer;touch-action:manipulation}button:hover{background:#edf5f7}button:focus-visible,select:focus-visible{outline:3px solid #387b99;outline-offset:3px}button:disabled{opacity:.4;cursor:default}.modes{display:grid;grid-template-columns:repeat(3,1fr);gap:7px}.modes button{font-size:14px;padding:13px 3px}.modes button[aria-pressed=true]{background:#294d60;color:white;border-color:#294d60}.brief{padding:18px 0 12px;min-height:124px}.brief h2{font-size:19px;margin:0 0 8px}.brief p{margin:0;line-height:1.7;font-size:14px;color:#506674}.level-row{font-size:13px}.level-row select{padding:7px;max-width:220px}.board-wrap{width:100%;aspect-ratio:1;max-height:590px}canvas{display:block;width:100%;height:100%;touch-action:manipulation}#message{min-height:44px;margin:0 0 12px;text-align:center;font-size:14px;line-height:1.6}.controls{display:grid;grid-template-columns:repeat(5,1fr);gap:7px}.controls button{padding:12px 3px;font-size:14px}#next{width:100%;margin-top:12px;background:#294d60;color:#fff}details{margin-top:20px;font-size:12px;color:#657986}#pieces{display:flex;gap:8px;flex-wrap:wrap;padding-top:10px}footer{font-size:12px;color:#657986;text-align:center;line-height:1.9;margin:24px 0 10px}@media(max-width:380px){main{padding:16px 12px}h1{font-size:24px}.modes button{font-size:12px}}