:root{font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;color:#253d35;background:#f5f7f2;font-synthesis:none;line-height:1.5}
*{box-sizing:border-box}body{margin:0}main{width:min(100%,560px);margin:auto;padding:24px 18px;padding-bottom:max(24px,env(safe-area-inset-bottom))}header{text-align:center;margin-bottom:24px}.eyebrow{font-size:.75rem;letter-spacing:.1em;font-weight:700;color:#52675e}h1{font-size:2rem;margin:8px 0}header p{margin:6px 0}section#exercise,section#finish{background:white;border:1px solid #d8e1d7;border-radius:24px;padding:22px;text-align:center;box-shadow:0 6px 24px #253d3508}#progress{color:#52675e;margin:0}#question{font-size:clamp(2.5rem,10vw,3.5rem);line-height:1.2;margin:24px 0}#answer-label{margin:0 0 14px}#answers{display:grid;grid-template-columns:1fr 1fr;gap:12px}button{font:inherit;font-weight:650;min-height:56px;border-radius:14px;border:2px solid transparent;padding:12px 16px;cursor:pointer;touch-action:manipulation;-webkit-tap-highlight-color:transparent}button:focus-visible{outline:3px solid #a24c00;outline-offset:4px}#answers button{font-size:1.8rem;min-height:76px;background:#edf3ed;border-color:#bbcdbf;color:#253d35}#answers button:disabled{opacity:1;cursor:default}#answers button.correct{background:#dceede;border-color:#39714d}#answers button.retry{border-color:#a86b35;background:#fff2df}.primary,.secondary{width:100%;margin-top:12px}.primary{color:white;background:#2f6248}.secondary{background:white;color:#2f6248;border-color:#a9bfb0}#feedback{min-height:3em;margin:16px 0 0;display:flex;align-items:center;justify-content:center}#help{margin-top:20px;padding-top:12px;border-top:1px solid #d8e1d7;text-align:left}h3{font-size:1.25rem;margin:12px 0}#help-text{margin:10px 0 16px}.frame-group{margin:16px 0}.frame-label{font-weight:600;margin:8px 0}.ten-frame{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:5px;border:2px solid #718779;border-radius:10px;padding:6px;max-width:320px}.cell{aspect-ratio:1;min-width:0;border:1px solid #bac9be;border-radius:5px;display:grid;place-items:center;background:#fafcf8}.dot{width:72%;height:72%;border-radius:50%;background:#315a89}.dot.added{background:#b45e19;border-radius:3px}.legend{font-size:.9rem}.key{display:inline-block;width:12px;height:12px;background:#315a89;border-radius:50%;margin-right:5px}.key.added{background:#b45e19;border-radius:2px;margin-left:12px}.equation{font-size:1.4rem;font-weight:700}footer{text-align:center;color:#52675e;font-size:.75rem;margin:24px 0}.finish-symbol{font-size:3rem;color:#39714d}#finish h2{font-size:1.8rem}[hidden]{display:none!important}@media(max-width:360px){main{padding:16px 12px}section#exercise,section#finish{padding:18px 14px}.ten-frame{gap:4px;padding:5px}}@media(prefers-reduced-motion:no-preference){button{transition:background-color .15s}}