html,
body {
  margin: 0;
  height: 100%;
  background: #0b0f14;
  color: #e7e9ee;
  font-family: system-ui, sans-serif;
  overflow: hidden;
  touch-action: none;
  user-select: none;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
}

.hud {
  display: flex;
  gap: 24px;
}

#board {
  --size: min(90vw, 78vh);
  --gap: calc(var(--size) * 0.025);
  width: var(--size);
  height: var(--size);
  box-sizing: border-box;
  padding: var(--gap);
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
  background: #111823;
  border-radius: 8px;
}

.cell {
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 6px;
  background: #1a2433;
  font-weight: 800;
  font-size: calc(var(--size) * 0.1);
  color: #0b0f14;
}

.cell.long {
  font-size: calc(var(--size) * 0.075);
}

.cell.longer {
  font-size: calc(var(--size) * 0.058);
}

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

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

@keyframes appear {
  from {
    transform: scale(0.3);
    opacity: 0;
  }
}

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

#message {
  margin: 0;
  min-height: 1.5em;
  color: #9aa1b2;
  text-align: center;
}