:root {
  color-scheme: light dark;
  font-family: "Yu Gothic", "Hiragino Kaku Gothic ProN", Meiryo, sans-serif;
  --bg: #f2f4f8;
  --fg: #222;
  --accent: #2979ff;
  --accent-dark: #1a5fd2;
  --board-bg: #fff;
  --border: #d0d7de;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 1.5rem;
  background: var(--bg);
  color: var(--fg);
}

.app {
  display: grid;
  gap: 1.25rem;
  padding: 2rem;
  background: var(--board-bg);
  border-radius: 1.25rem;
  box-shadow: 0 20px 45px rgba(0, 0, 0, 0.15);
  max-width: 420px;
  width: min(90vw, 420px);
}

.title {
  margin: 0;
  text-align: center;
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  letter-spacing: 0.05em;
}

.board {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
}

.cell {
  position: relative;
  width: 100%;
  padding-top: 100%;
  border: 2px solid var(--border);
  border-radius: 0.75rem;
  background: transparent;
  font-size: clamp(2.5rem, 8vw, 3.5rem);
  font-weight: 700;
  color: var(--accent);
  cursor: pointer;
  transition: transform 0.18s ease, box-shadow 0.18s ease, color 0.18s ease;
}

.cell[disabled],
.cell.filled {
  cursor: not-allowed;
}

.cell span {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.cell:not([disabled]):hover,
.cell:not([disabled]):focus-visible {
  transform: translateY(-2px);
  box-shadow: 0 10px 20px rgba(41, 121, 255, 0.18);
  border-color: var(--accent);
  outline: none;
}

.cell.win {
  background: rgba(41, 121, 255, 0.12);
  border-color: var(--accent);
  color: var(--accent-dark);
}

.status {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  align-items: center;
}

.message {
  margin: 0;
  font-size: 1.1rem;
}

.reset {
  padding: 0.6rem 1.5rem;
  border-radius: 999px;
  border: none;
  background: var(--accent);
  color: #fff;
  font-weight: 600;
  letter-spacing: 0.05em;
  cursor: pointer;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.reset:hover,
.reset:focus-visible {
  transform: translateY(-1px);
  box-shadow: 0 12px 25px rgba(41, 121, 255, 0.25);
  outline: none;
}

.reset:active {
  transform: translateY(0);
  box-shadow: none;
}

.footer {
  font-size: 0.85rem;
  color: rgba(0, 0, 0, 0.55);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d1117;
    --fg: #e6edf3;
    --board-bg: #161b22;
    --border: #30363d;
  }

  .footer {
    color: rgba(255, 255, 255, 0.55);
  }
}