:root {
  --bg: #f8fafc;
  --card: #ffffff;
  --line: #dbe2ea;
  --text: #0f172a;
  --accent: #0ea5e9;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-items: center;
  font-family: "Avenir Next", "Segoe UI", sans-serif;
  background: radial-gradient(circle at top, #e0f2fe, var(--bg));
  color: var(--text);
}

.app {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 24px;
  width: min(92vw, 420px);
  text-align: center;
  box-shadow: 0 12px 40px rgba(15, 23, 42, 0.08);
}

h1 { margin: 0 0 8px; }

#status { margin: 0 0 18px; font-weight: 600; }

.board {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}

.cell {
  aspect-ratio: 1;
  font-size: clamp(1.8rem, 7vw, 2.7rem);
  font-weight: 700;
  border: 2px solid var(--line);
  border-radius: 12px;
  background: #f8fbff;
  color: var(--text);
  cursor: pointer;
}

.cell:disabled {
  cursor: not-allowed;
  opacity: 0.9;
}

.reset {
  margin-top: 18px;
  border: none;
  border-radius: 10px;
  padding: 10px 14px;
  background: var(--accent);
  color: white;
  font-weight: 700;
  cursor: pointer;
}