/* ---------- Layout & theme ---------- */

:root {
  --bg: #faf8ef;
  --text: #776e65;
  --muted: #a39489;
  --accent: #8f7a66;
  --accent-hover: #9c8975;
  --board-bg: #bbada0;
  --cell-bg: rgba(238, 228, 218, 0.35);
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.08);

  --grid-size: 4;
  --cell-size: 92px;
  --gap: 12px;
  --board-size: calc(var(--grid-size) * var(--cell-size) + (var(--grid-size) + 1) * var(--gap));
  --slide-ms: 120ms;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: 'Clear Sans', 'Helvetica Neue', Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
}

.app {
  max-width: 520px;
  margin: 0 auto;
  padding: 32px 16px 48px;
  display: flex;
  flex-direction: column;
  gap: 18px;
}

/* ---------- Header ---------- */

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

h1 {
  margin: 0;
  font-size: 56px;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text);
}

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

.score-box {
  background: var(--board-bg);
  color: white;
  padding: 8px 14px;
  border-radius: 6px;
  min-width: 72px;
  text-align: center;
  display: flex;
  flex-direction: column;
}

.score-box .label {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  opacity: 0.85;
}

.score-box .value {
  font-size: 22px;
  font-weight: 700;
  line-height: 1.1;
}

/* ---------- Controls ---------- */

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

.target-select {
  font-size: 14px;
  color: var(--text);
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

.target-select select {
  font-size: 14px;
  padding: 4px 10px;
  border: 1px solid var(--muted);
  border-radius: 4px;
  background: white;
  color: var(--text);
}

#new-game {
  background: var(--accent);
  color: white;
  border: none;
  border-radius: 4px;
  padding: 10px 18px;
  font-size: 15px;
  font-weight: 700;
  cursor: pointer;
  transition: background 100ms ease-in-out;
}

#new-game:hover,
#new-game:focus-visible {
  background: var(--accent-hover);
}

/* ---------- Message banner ---------- */

.message {
  padding: 10px 14px;
  border-radius: 4px;
  font-size: 14px;
  font-weight: 600;
}

.message[data-mode='win'] {
  background: #f9f6f2;
  color: #8f7a66;
  border-left: 4px solid #edc22e;
}

.message[data-mode='lose'] {
  background: #f9f6f2;
  color: #8f7a66;
  border-left: 4px solid #f65e3b;
}

/* ---------- Board ---------- */

.board {
  position: relative;
  width: var(--board-size);
  height: var(--board-size);
  background: var(--board-bg);
  border-radius: 8px;
  padding: var(--gap);
  touch-action: none;
  outline: none;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.grid-bg {
  position: absolute;
  inset: var(--gap);
  display: grid;
  grid-template-columns: repeat(var(--grid-size), var(--cell-size));
  grid-template-rows: repeat(var(--grid-size), var(--cell-size));
  gap: var(--gap);
}

.grid-cell {
  background: var(--cell-bg);
  border-radius: 4px;
}

.tiles {
  position: absolute;
  inset: var(--gap);
  pointer-events: none;
}

/* ---------- Tiles ---------- */

.tile {
  position: absolute;
  width: var(--cell-size);
  height: var(--cell-size);
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 36px;
  font-weight: 800;
  color: var(--text);
  background: #eee4da;
  box-shadow: var(--shadow);
  transform: translate(
    calc(var(--col, 0) * (var(--cell-size) + var(--gap))),
    calc(var(--row, 0) * (var(--cell-size) + var(--gap)))
  );
  transition: transform var(--slide-ms) ease-in-out;
}

.tile.tile-appear {
  animation: tile-appear var(--slide-ms) ease-in-out;
}

.tile.tile-pop {
  animation: tile-pop var(--slide-ms) ease-in-out;
  z-index: 1;
}

@keyframes tile-appear {
  0% { transform: translate(
        calc(var(--col, 0) * (var(--cell-size) + var(--gap))),
        calc(var(--row, 0) * (var(--cell-size) + var(--gap)))
      ) scale(0); }
  100% { transform: translate(
        calc(var(--col, 0) * (var(--cell-size) + var(--gap))),
        calc(var(--row, 0) * (var(--cell-size) + var(--gap)))
      ) scale(1); }
}

@keyframes tile-pop {
  0% { transform: translate(
        calc(var(--col, 0) * (var(--cell-size) + var(--gap))),
        calc(var(--row, 0) * (var(--cell-size) + var(--gap)))
      ) scale(1); }
  50% { transform: translate(
        calc(var(--col, 0) * (var(--cell-size) + var(--gap))),
        calc(var(--row, 0) * (var(--cell-size) + var(--gap)))
      ) scale(1.18); }
  100% { transform: translate(
        calc(var(--col, 0) * (var(--cell-size) + var(--gap))),
        calc(var(--row, 0) * (var(--cell-size) + var(--gap)))
      ) scale(1); }
}

.tile-v2 { background: #eee4da; color: #776e65; }
.tile-v4 { background: #ede0c8; color: #776e65; }
.tile-v8 { background: #f2b179; color: white; }
.tile-v16 { background: #f59563; color: white; }
.tile-v32 { background: #f67c5f; color: white; }
.tile-v64 { background: #f65e3b; color: white; }
.tile-v128 { background: #edcf72; color: white; font-size: 30px; }
.tile-v256 { background: #edcc61; color: white; font-size: 30px; }
.tile-v512 { background: #edc850; color: white; font-size: 30px; }
.tile-v1024 { background: #edc53f; color: white; font-size: 24px; }
.tile-v2048 { background: #edc22e; color: white; font-size: 24px; }
.tile-v4096,
.tile-v8192 { background: #3c3a32; color: white; font-size: 22px; }

/* ---------- Hint and footer ---------- */

.hint {
  font-size: 13px;
  color: var(--muted);
  text-align: center;
  margin: 4px 0 0;
}

.footer {
  margin-top: 8px;
  text-align: center;
  font-size: 12px;
  color: var(--muted);
}

.footer a {
  color: var(--muted);
  text-decoration: none;
  border-bottom: 1px dotted var(--muted);
}

/* ---------- Responsive ---------- */

@media (max-width: 520px) {
  :root {
    --cell-size: calc((100vw - 80px) / 4);
    --gap: 8px;
  }
  h1 { font-size: 40px; }
  .tile { font-size: 28px; }
  .tile-v128, .tile-v256, .tile-v512 { font-size: 24px; }
  .tile-v1024, .tile-v2048 { font-size: 20px; }
}