:root{--bg: #0f172a;--card: #1e293b;--accent: #38bdf8;--good: #22c55e;--bad: #ef4444;--warn: #f59e0b;--text: #f1f5f9;--muted: #94a3b8}*{box-sizing:border-box;margin:0;padding:0}html{-webkit-text-size-adjust:100%}body{font-family:Trebuchet MS,Segoe UI,system-ui,sans-serif;background:radial-gradient(circle at top,#1e293b,#0f172a);background-attachment:fixed;color:var(--text);min-height:100vh;min-height:100dvh;-webkit-tap-highlight-color:transparent}.app{max-width:560px;margin:0 auto;padding:calc(20px + env(safe-area-inset-top)) calc(16px + env(safe-area-inset-right)) calc(32px + env(safe-area-inset-bottom)) calc(16px + env(safe-area-inset-left));display:flex;flex-direction:column;gap:20px}.hud{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}.stat{background:var(--card);border-radius:16px;padding:10px 6px;text-align:center;box-shadow:0 4px 12px #00000040;min-width:0}.stat__label{display:block;font-size:.75rem;text-transform:uppercase;letter-spacing:.08em;color:var(--muted)}.stat__value{display:block;font-size:1.4rem;font-weight:800;margin-top:4px;white-space:nowrap}.card{background:var(--card);border-radius:24px;padding:28px 24px 32px;box-shadow:0 12px 32px #00000059;display:flex;flex-direction:column;gap:22px}.timer{position:relative;height:28px;background:#0f172a;border-radius:999px;overflow:hidden}.timer__bar{height:100%;background:linear-gradient(90deg,var(--good),var(--accent));transition:width .1s linear}.timer--danger .timer__bar{background:linear-gradient(90deg,var(--warn),var(--bad))}.timer__label{position:absolute;top:0;right:0;bottom:0;left:0;display:flex;align-items:center;justify-content:center;font-weight:700;font-size:.9rem;text-shadow:0 1px 2px rgba(0,0,0,.6)}.problem{font-size:clamp(3rem,14vw,5rem);font-weight:900;text-align:center;letter-spacing:.02em}.problem .x{color:var(--accent)}.answer{display:flex;flex-direction:column;gap:12px}.answer input{width:100%;font-size:2rem;font-weight:800;text-align:center;padding:12px;border:3px solid #334155;border-radius:16px;background:#0f172a;color:var(--text);outline:none}.answer input:focus{border-color:var(--accent)}.answer input::-webkit-outer-spin-button,.answer input::-webkit-inner-spin-button{-webkit-appearance:none;margin:0}.answer input[type=number]{-moz-appearance:textfield}button{font-family:inherit;cursor:pointer;border:none;border-radius:16px;font-weight:800;font-size:1.1rem;padding:12px 20px;background:var(--accent);color:#06283d;transition:transform .05s ease,opacity .15s ease}button:active{transform:scale(.97)}button:disabled{opacity:.4;cursor:not-allowed}.hint{text-align:center;color:var(--muted);font-size:.85rem}.feedback{display:flex;flex-direction:column;gap:18px;text-align:center}.feedback__banner{font-size:1.6rem;font-weight:900;padding:12px;border-radius:16px}.feedback--good .feedback__banner{background:#22c55e26;color:var(--good)}.feedback--bad .feedback__banner{background:#ef444426;color:var(--bad)}.feedback__equation{font-size:2rem;font-weight:800}.trick{background:#0f172a;border-radius:16px;padding:18px;text-align:left}.trick__title{font-weight:800;font-size:1.1rem;margin-bottom:10px}.trick__intro{color:var(--muted);line-height:1.5;margin-bottom:12px}.trick__steps{list-style:none;display:flex;flex-direction:column;gap:6px;margin-bottom:12px}.trick__steps li{background:#1e293b;padding:8px 12px;border-radius:10px;font-weight:700;font-size:1.05rem}.trick__sum{font-size:1.15rem;font-weight:800;border-top:2px dashed #334155;padding-top:12px}.next{align-self:center;background:var(--good);color:#052e16;padding:14px 28px;font-size:1.2rem}.start{align-items:center;text-align:center;padding-top:48px}.start__title{font-size:clamp(2.4rem,10vw,3.4rem);font-weight:900}.start__sub{color:var(--muted);font-size:1rem}.start__card{width:100%;align-items:stretch}.start__label{font-weight:800;text-transform:uppercase;letter-spacing:.08em;font-size:.8rem;color:var(--muted)}.start__presets{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}.preset{background:#0f172a;color:var(--text);border:3px solid #334155;padding:14px 0;font-size:1.2rem}.preset--on{border-color:var(--accent);background:#38bdf826;color:var(--accent)}.start__input{font-size:1.6rem;font-weight:800;text-align:center;padding:12px;border:3px solid #334155;border-radius:16px;background:#0f172a;color:var(--text);outline:none}.start__input:focus{border-color:var(--accent)}.start__input::-webkit-outer-spin-button,.start__input::-webkit-inner-spin-button{-webkit-appearance:none;margin:0}.start__input[type=number]{-moz-appearance:textfield}.progress{position:relative;height:26px;background:var(--card);border-radius:999px;overflow:hidden;box-shadow:0 4px 12px #00000040}.progress__bar{height:100%;background:linear-gradient(90deg,var(--accent),var(--good));transition:width .4s ease}.progress__bar--gold{background:linear-gradient(90deg,#f59e0b,#fde047)}.progress__label{position:absolute;top:0;right:0;bottom:0;left:0;display:flex;align-items:center;justify-content:center;font-weight:700;font-size:.85rem;text-shadow:0 1px 2px rgba(0,0,0,.6)}.restart{align-self:center;background:transparent;color:var(--muted);font-size:.85rem;font-weight:700;padding:6px 12px}.overlay{position:fixed;top:0;right:0;bottom:0;left:0;background:#020617cc;-webkit-backdrop-filter:blur(4px);backdrop-filter:blur(4px);display:flex;align-items:center;justify-content:center;padding:24px;z-index:10;animation:fade .2s ease}.celebrate{background:var(--card);border:4px solid var(--good);border-radius:24px;padding:32px 28px;max-width:440px;width:100%;text-align:center;display:flex;flex-direction:column;gap:16px;box-shadow:0 20px 50px #00000080;animation:pop .35s cubic-bezier(.18,.89,.32,1.28)}.celebrate--gold{border-color:#fde047}.celebrate__emoji{font-size:3.4rem}.celebrate__title{font-size:2rem;font-weight:900}.celebrate__sub{color:var(--muted);line-height:1.5}@keyframes pop{0%{transform:scale(.7);opacity:0}to{transform:scale(1);opacity:1}}@keyframes fade{0%{opacity:0}to{opacity:1}}@media (max-width: 430px){.app{gap:16px}.hud{grid-template-columns:repeat(2,1fr)}.stat__value{font-size:1.5rem}.card{padding:22px 18px 26px;border-radius:20px}.problem{font-size:clamp(3.2rem,18vw,4.5rem)}.answer input{font-size:1.8rem;padding:14px 10px}button{padding:14px 16px}.start__presets{gap:8px}.preset{padding:16px 0}}@media (pointer: coarse){button,.answer input,.start__input,.preset{min-height:52px}}