:root{color-scheme:dark;--bg:#0a101a;--panel:#151e2d;--ink:#f4f7ff;--muted:#aebbd0;--mint:#69efc3;--coral:#ff8e93;--line:#29374c}*{box-sizing:border-box}body{margin:0;background:radial-gradient(ellipse at 75% 6%,#163637,transparent 35rem),var(--bg);color:var(--ink);font:17px/1.6 system-ui,sans-serif}a{color:var(--mint);text-underline-offset:.24em}a:focus-visible,summary:focus-visible{outline:2px solid var(--mint);outline-offset:5px}header,main,footer{max-width:1120px;margin:auto;padding-inline:clamp(18px,5vw,48px)}header,footer{display:flex;align-items:center;justify-content:space-between;gap:16px;flex-wrap:wrap;padding-block:24px}header{border-bottom:1px solid var(--line)}header a{text-decoration:none;font-weight:750}nav{display:flex;gap:20px;flex-wrap:wrap}.brand{display:flex;align-items:center;gap:10px;color:var(--ink)}.brand img{border-radius:10px}h1,h2,h3{line-height:1.08;margin:0 0 .55em;font-weight:850;letter-spacing:-.04em}h1{font-size:clamp(3rem,8vw,6.8rem)}h2{font-size:clamp(2rem,4vw,3.4rem)}h3{font-size:1.35rem}p{margin:.6em 0 1.2em;color:var(--muted)}.hero{display:grid;grid-template-columns:1.15fr 1fr;align-items:center;gap:clamp(25px,6vw,70px);padding:clamp(44px,8vw,100px) 0}.eyebrow{font-size:.8rem;letter-spacing:.16em;text-transform:uppercase;font-weight:800;color:var(--mint)}.actions{display:flex;gap:12px;align-items:center;flex-wrap:wrap}.button,.badge{display:inline-flex;align-items:center;gap:9px;border-radius:12px;padding:10px 16px;font-weight:760;text-decoration:none}.button{background:var(--mint);color:#0b211c}.badge{border:1px solid var(--line);background:#0a0e17;color:var(--ink)}.badge small{display:block;color:var(--muted);font-size:.72rem;line-height:1}.badge svg{width:24px;height:24px;fill:none;stroke:var(--mint);stroke-width:1.7}.section{padding:48px 0;border-top:1px solid var(--line)}.intro{max-width:700px}.cards,.steps{display:grid;grid-template-columns:repeat(3,1fr);gap:16px}.card,details{padding:22px;border:1px solid var(--line);background:var(--panel);border-radius:20px}.card p,details p{margin-bottom:0}.card .eyebrow{display:block;margin-bottom:12px}.board,.mini{display:grid;grid-template-columns:repeat(3,minmax(0,1fr))}.board{aspect-ratio:1;gap:7px;padding:9px;border:1px solid var(--line);border-radius:18px;background:#0d1521;max-width:420px;margin-inline:auto;width:100%}.mini{position:relative;gap:3px;padding:5px;background:#202c3e;border-radius:8px}.mini span,.mini b{display:grid;place-items:center;color:var(--coral);font-weight:900;background:#151e2d;border-radius:3px;font-size:clamp(9px,1.7vw,20px);line-height:1}.mini .o,.mini b.o{color:var(--mint)}.mini.active{outline:2px solid var(--mint);background:#254b47}.mini b{position:absolute;inset:5px;font-size:clamp(20px,4vw,50px)}.mini b.win{background:#402b3c;outline:1px solid var(--coral)}.board.small{max-width:190px;gap:4px;padding:5px}.board.small .mini{padding:3px;gap:2px}.diagram{margin:0}.diagram figcaption{text-align:center;color:var(--muted);margin-top:12px;font-size:.85rem}.step .diagram{margin:16px 0}.steps{list-style:none;padding:0}.sample{max-width:96px}.sample .mini{aspect-ratio:1}.qa{display:grid;gap:10px}summary{cursor:pointer;font-weight:730}footer{border-top:1px solid var(--line);color:var(--muted);font-size:.9rem}.skip{position:absolute;left:-999px}.skip:focus{left:12px;top:12px;background:var(--panel);padding:10px;z-index:2}@media(max-width:740px){.hero{grid-template-columns:1fr}.hero .diagram{max-width:400px;width:100%;justify-self:center}.cards,.steps{grid-template-columns:1fr}.board.small .mini span{font-size:10px}}@media(min-width:741px) and (max-width:950px){.steps{grid-template-columns:repeat(2,1fr)}} 
.game-title-line{display:inline-block;white-space:nowrap;font-size:.85em}
@media(max-width:740px){.game-title-line{font-size:min(.85em,12vw)}}

.demo-board,.demo-board .mini{grid-template-rows:repeat(3,minmax(0,1fr))}
.demo-board,.demo-board .mini,.demo-board .cell{border-radius:0}
.demo-board .mini,.demo-board .cell{min-width:0;min-height:0}
.demo-board .cell b{position:static;inset:auto;background:none;font-size:inherit;line-height:1;color:inherit}
.demo-target{outline:2px solid var(--mint);outline-offset:-2px}
@media(prefers-reduced-motion:no-preference){
.demo-source{animation:source-board 9s step-end 2}
.demo-target{animation:target-board 9s step-end 2}
.demo-x{animation:chosen-square 9s step-end 2}
.demo-x b{animation:place-x 9s step-end 2}
.demo-o b{animation:place-o 9s step-end 2}
@keyframes source-board{0%,100%{outline:2px solid var(--coral);outline-offset:-2px}40%{outline-color:transparent}}
@keyframes target-board{0%{outline-color:transparent}40%,100%{outline-color:var(--mint);background:#254b47}}
@keyframes chosen-square{0%{background:#683847}24%,100%{background:#151e2d}}
@keyframes place-x{0%{opacity:0}24%,100%{opacity:1}}
@keyframes place-o{0%{opacity:0}74%,100%{opacity:1}}
}