:root{color-scheme:light;font-family:Segoe UI,system-ui,-apple-system,sans-serif;line-height:1.5;font-weight:400;background-color:#f5f5fb;color:#0f172a}*{box-sizing:border-box}body{margin:0;background:radial-gradient(circle at top,#fff,#eef2ff 60%,#f5f5fb)}.app{max-width:1100px;margin:0 auto;padding:40px 20px 64px}header{text-align:center;margin-bottom:32px}header h1{font-size:clamp(2rem,3vw,2.8rem);margin:10px 0 6px}header p{margin:0;color:#475569}.badge{display:inline-block;padding:6px 14px;border-radius:999px;background:#e0e7ff;color:#4338ca;font-weight:600;font-size:.85rem;text-transform:uppercase;letter-spacing:.05em}.layout{display:grid;grid-template-columns:minmax(0,1.7fr) minmax(0,1fr);gap:24px;align-items:start}.board{background:#fff;border-radius:24px;padding:24px;box-shadow:0 16px 30px #0f172a1f}.image-frame{position:relative;width:100%;aspect-ratio:1 / 1;border-radius:18px;overflow:hidden;background:#e2e8f0}.image-frame img{width:100%;height:100%;object-fit:cover;display:block}.tile-grid{position:absolute;inset:0;display:grid;grid-template-columns:repeat(4,1fr);grid-template-rows:repeat(4,1fr);gap:0}.tile{border:1px solid #e2e8f0;background:#fff;display:flex;flex-direction:column;justify-content:center;align-items:center;padding:10px;transition:opacity .25s ease,transform .25s ease;text-align:center;font:inherit;color:inherit;cursor:pointer}.tile.revealed,.tile.locked{background:#fff}.tile.cleared{opacity:0;pointer-events:none}.tile.shake{animation:shake .3s ease}.problem{font-weight:700;margin-bottom:8px;color:#1e293b}.tile input{width:80px;max-width:90%;padding:6px 8px;border-radius:8px;border:1px solid #cbd5f5;font-size:1rem;text-align:center;background:#fff}.tile input:disabled{opacity:.75;cursor:not-allowed}.feedback{margin-top:6px;font-size:.85rem;color:#dc2626;min-height:1.1em}.tile.cleared .feedback{color:#16a34a}.complete-overlay{position:absolute;inset:0;background:#0f172a99;color:#fff;display:flex;align-items:center;justify-content:center;text-align:center;padding:20px;opacity:0;pointer-events:none;transition:opacity .3s ease}.complete-overlay.show{opacity:1;pointer-events:auto}.complete-overlay h2{margin:0 0 6px}.sidebar{display:grid;gap:16px}.panel{background:#fff;border-radius:20px;padding:20px;box-shadow:0 12px 24px #0f172a14}.panel h2,.panel h3{margin:0 0 10px}.progress-text{margin:0;font-size:1.1rem;font-weight:600}.mastery-text{margin:8px 0 0;color:#1e293b;font-weight:600}.mastery-hint{margin:8px 0 0;font-size:.92rem;color:#64748b}.divider{height:1px;background:#e2e8f0;margin:16px 0}.panel-actions{display:grid;gap:8px}.primary,.secondary{width:100%;border:none;padding:10px 16px;border-radius:10px;font-size:1rem;font-weight:600;cursor:pointer}.primary{background:#4f46e5;color:#fff}.primary:hover{background:#4338ca}.secondary{background:#e0e7ff;color:#3730a3}.secondary:hover{background:#c7d2fe}.hint{margin-top:12px;font-size:.92rem;color:#64748b}.tips ul{margin:0;padding-left:18px;color:#475569}@keyframes shake{0%{transform:translate(0)}25%{transform:translate(-3px)}50%{transform:translate(3px)}75%{transform:translate(-2px)}to{transform:translate(0)}}@media(max-width:900px){.layout{grid-template-columns:1fr}}@media(max-width:600px){.tile input{width:64px}}