:root {
  --bg: #07070f;
  --surface: #11111f;
  --surface-2: #1a1a2e;
  --line: #2a2a45;
  --ink: #ecebff;
  --muted: #9a98c3;
  --neon: #22e3ff;
  --pink: #ff3ec8;
  --gap: clamp(6px, 2.2vmin, 12px);
  /* Chừa chỗ cho tiêu đề, thanh nút và dòng kết quả dưới bàn chơi để khung game không phải cuộn */
  --size: min(92vw, calc(100vh - 215px), 460px);
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  height: 100%;
  background: var(--bg);
  color: var(--ink);
  font-family: "Segoe UI", system-ui, -apple-system, sans-serif;
  -webkit-user-select: none;
  user-select: none;
  overscroll-behavior: none;
  /* Nếu màn quá thấp vẫn phải cuộn thì dùng thanh cuộn tối, không hiện thanh trắng mặc định */
  scrollbar-width: thin;
  scrollbar-color: var(--line) var(--bg);
  color-scheme: dark;
}

.app {
  width: var(--size);
  margin: 0 auto;
  padding: 14px 0 10px;
}

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

.title {
  margin: 0;
  font-size: clamp(32px, 9vmin, 52px);
  font-weight: 800;
  letter-spacing: 1px;
  background: linear-gradient(90deg, var(--neon), var(--pink));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

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

.box {
  min-width: 72px;
  padding: 6px 12px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--surface);
  text-align: center;
}

.label {
  display: block;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
}

.value {
  display: block;
  font-size: 18px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin: 12px 0;
}

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

.btn {
  flex-shrink: 0;
  border: 0;
  border-radius: 10px;
  padding: 9px 16px;
  font: inherit;
  font-weight: 700;
  font-size: 14px;
  color: var(--bg);
  background: linear-gradient(90deg, var(--neon), var(--pink));
  cursor: pointer;
}

.btn:hover {
  filter: brightness(1.1);
}

.btn.ghost {
  color: var(--ink);
  background: var(--surface-2);
  border: 1px solid var(--line);
}

.board {
  position: relative;
  width: var(--size);
  height: var(--size);
  padding: var(--gap);
  border-radius: 14px;
  background: var(--surface);
  border: 1px solid var(--line);
  touch-action: none;
}

.grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
  width: 100%;
  height: 100%;
}

.cell {
  display: grid;
  place-items: center;
  border-radius: 10px;
  background: var(--surface-2);
  font-weight: 800;
  font-size: calc(var(--size) / 9);
  font-variant-numeric: tabular-nums;
}

.cell.tile {
  color: var(--bg);
}

.cell.small {
  font-size: calc(var(--size) / 12);
}

.cell.tiny {
  font-size: calc(var(--size) / 15);
}

.cell.new {
  animation: pop-in 140ms ease-out;
}

.cell.merged {
  animation: pop 160ms ease-out;
}

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

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

/* Màu ô theo giá trị */
.tile.v2 { background: #2b2b4a; color: var(--ink); }
.tile.v4 { background: #343463; color: var(--ink); }
.tile.v8 { background: #1f6f8b; color: #fff; }
.tile.v16 { background: #168aad; color: #fff; }
.tile.v32 { background: #1ea7c9; }
.tile.v64 { background: #22e3ff; }
.tile.v128 { background: #7b5cff; color: #fff; box-shadow: 0 0 14px rgb(123 92 255 / 0.5); }
.tile.v256 { background: #9d4dff; color: #fff; box-shadow: 0 0 16px rgb(157 77 255 / 0.55); }
.tile.v512 { background: #c63cff; color: #fff; box-shadow: 0 0 18px rgb(198 60 255 / 0.6); }
.tile.v1024 { background: #ff3ec8; color: #fff; box-shadow: 0 0 20px rgb(255 62 200 / 0.6); }
.tile.v2048 { background: linear-gradient(135deg, #22e3ff, #ff3ec8); color: #07070f; box-shadow: 0 0 26px rgb(255 62 200 / 0.7); }
.tile.vbig { background: #b6ff3b; color: #07070f; box-shadow: 0 0 26px rgb(182 255 59 / 0.6); }

.overlay {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 20px;
  border-radius: 14px;
  background: rgb(7 7 15 / 0.82);
  backdrop-filter: blur(3px);
  text-align: center;
}

.overlay-title {
  margin: 0;
  font-size: clamp(26px, 7vmin, 38px);
  font-weight: 800;
}

.overlay-text {
  margin: 0 0 10px;
  color: var(--muted);
}

.overlay-actions {
  display: flex;
  gap: 10px;
}

.result {
  margin: 12px 0 0;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--line);
  background: var(--surface);
  font-size: 13px;
  text-align: center;
}

.result.ok {
  border-color: rgb(182 255 59 / 0.5);
  color: #b6ff3b;
}

.result.err {
  border-color: rgb(255 62 200 / 0.5);
  color: var(--pink);
}

.note {
  margin: 12px 0 0;
  font-size: 12px;
  color: var(--muted);
  text-align: center;
}

.hidden {
  display: none !important;
}