:root{color-scheme:light;font-family:system-ui,-apple-system,"PingFang SC",sans-serif;background:#f5f7fa;color:#17212b}
*{box-sizing:border-box}
body{min-height:100vh;margin:0;display:grid;place-items:center;padding:24px}
main{width:min(100%,430px);padding:36px 30px;background:#fff;border:1px solid #dce3eb;border-radius:18px;box-shadow:0 16px 50px #18253614}
h1{font-size:1.55rem;margin:0 0 12px}
p{line-height:1.6;color:#506070;margin:0 0 24px}
#challenge{min-height:68px}
button{width:100%;margin-top:20px;padding:14px;background:#174ed7;color:#fff;border:0;border-radius:9px;font:inherit;font-weight:600;cursor:pointer}
button:disabled{background:#aab5c2;cursor:default}
#status{margin:16px 0 0;min-height:1.5em;font-size:.9rem;color:#b02f2f}