:root {
  --bg: #0d1117;
  --panel: #161b22;
  --border: #30363d;
  --ink: #e6edf3;
  --muted: #8b949e;
  --accent: #58a6ff;
  --x: #ff7b72;
  --o: #79c0ff;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--ink);
  font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;
  line-height: 1.5;
}

.game {
  width: min(100%, 420px);
  margin: 0 auto;
  padding: 24px 16px 40px;
}

h1 {
  margin: 0 0 8px;
  font-size: 2rem;
}

.options {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin: 0 0 16px;
}

fieldset {
  flex: 1 1 120px;
  margin: 0;
  padding: 8px 12px 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
}

fieldset:disabled {
  opacity: 0.5;
}

legend {
  padding: 0 4px;
  color: var(--muted);
  font-size: 0.85rem;
}

fieldset label {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 2px 0;
  cursor: pointer;
}

input[type="radio"] {
  accent-color: var(--accent);
  width: 1.1em;
  height: 1.1em;
}

input:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 2px;
}

.scores {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px;
  margin: 0 0 12px;
  text-align: center;
}

.scores div {
  padding: 6px 4px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
}

.scores dt {
  color: var(--muted);
  font-size: 0.8rem;
}

.scores dd {
  margin: 0;
  font-size: 1.3rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.status {
  min-height: 1.5em;
  margin: 0 0 16px;
  font-weight: 600;
}

button {
  font: inherit;
  color: var(--ink);
  cursor: pointer;
}

button:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 3px;
}

.board {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px;
  width: 100%;
  aspect-ratio: 1;
}

.cell {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
  font-size: clamp(2.4rem, 16vw, 4rem);
  font-weight: 800;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
}

.cell[aria-disabled="true"] {
  cursor: default;
}

.cell.x {
  color: var(--x);
}

.cell.o {
  color: var(--o);
}

.cell.pop {
  animation: pop 180ms ease-out;
}

@keyframes pop {
  from {
    transform: scale(0.6);
    opacity: 0.2;
  }
  to {
    transform: scale(1);
    opacity: 1;
  }
}

.cell.win {
  background: #1f2f1f;
  border-color: #3fb950;
}

.help {
  margin: 12px 0 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.actions {
  display: flex;
  justify-content: center;
  margin-top: 16px;
}

.actions button {
  font-weight: 600;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 14px;
}

.actions button:hover {
  border-color: var(--accent);
}

@media (max-width: 400px) {
  .game {
    padding: 16px 12px 32px;
  }

  h1 {
    font-size: 1.7rem;
  }

  fieldset {
    flex-basis: 100%;
  }

  fieldset label {
    display: inline-flex;
    margin-right: 12px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .cell.pop {
    animation: none;
  }
}