:root {
  --bg: #0d1117;
  --panel: #161b22;
  --border: #30363d;
  --ink: #e6edf3;
  --muted: #8b949e;
  --accent: #58a6ff;
  --cell: #21262d;
}

* {
  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%, 440px);
  margin: 0 auto;
  padding: 24px 16px 40px;
}

.top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

h1 {
  margin: 0;
  font-size: 2.4rem;
  letter-spacing: -0.02em;
}

.scores {
  display: flex;
  gap: 8px;
}

.score-box {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 72px;
  padding: 4px 12px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
}

.score-box .label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
}

.score-box .value {
  font-weight: 700;
  font-size: 1.2rem;
  font-variant-numeric: tabular-nums;
}

.bar {
  display: flex;
  justify-content: flex-end;
  margin-top: 16px;
}

.actions {
  display: flex;
  gap: 8px;
}

button {
  font: inherit;
  font-weight: 600;
  color: var(--ink);
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 14px;
  cursor: pointer;
}

button:hover:not(:disabled) {
  border-color: var(--accent);
}

button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

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

.help {
  color: var(--muted);
  margin: 12px 0 16px;
  font-size: 0.95rem;
}

.board {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  padding: 10px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  aspect-ratio: 1;
  width: 100%;
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}

.tile {
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  background: var(--cell);
  font-weight: 700;
  font-size: clamp(1.1rem, 7vw, 2rem);
  color: #1b1b1b;
}

.tile-new {
  animation: pop-in 160ms ease-out;
}

.tile-merged {
  animation: bump 160ms ease-out;
}

@keyframes pop-in {
  from {
    transform: scale(0.4);
    opacity: 0;
  }
  to {
    transform: scale(1);
    opacity: 1;
  }
}

@keyframes bump {
  50% {
    transform: scale(1.12);
  }
}

.tile-2 { background: #eee4da; }
.tile-4 { background: #ede0c8; }
.tile-8 { background: #f2b179; color: #fff; }
.tile-16 { background: #f59563; color: #fff; }
.tile-32 { background: #f67c5f; color: #fff; }
.tile-64 { background: #f65e3b; color: #fff; }
.tile-128 { background: #edcf72; color: #fff; font-size: clamp(1rem, 6vw, 1.7rem); }
.tile-256 { background: #edcc61; color: #fff; font-size: clamp(1rem, 6vw, 1.7rem); }
.tile-512 { background: #edc850; color: #fff; font-size: clamp(1rem, 6vw, 1.7rem); }
.tile-1024 { background: #edc53f; color: #fff; font-size: clamp(0.85rem, 5vw, 1.4rem); }
.tile-2048 { background: #edc22e; color: #fff; font-size: clamp(0.85rem, 5vw, 1.4rem); }
.tile-super { background: #3c3a32; color: #fff; font-size: clamp(0.8rem, 4.5vw, 1.2rem); }

.board-wrap {
  position: relative;
}

.overlay {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 16px;
  padding: 16px;
  text-align: center;
  background: rgba(13, 17, 23, 0.82);
  border-radius: 12px;
}

.overlay[hidden] {
  display: none;
}

.overlay-text {
  margin: 0;
  font-size: 1.6rem;
  font-weight: 700;
}

.overlay-actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
}

.status {
  min-height: 1.5em;
  margin: 12px 0 0;
  color: var(--muted);
  text-align: center;
}

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

  h1 {
    font-size: 2rem;
  }

  .score-box {
    min-width: 60px;
    padding: 4px 8px;
  }

  .board {
    gap: 8px;
    padding: 8px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .tile-new,
  .tile-merged {
    animation: none;
  }
}