.board {
  --light: #eeeed2;
  --dark: #769656;
  --highlight: rgba(255, 255, 0, 0.5);
  --hint: rgba(0, 0, 0, 0.1);
  --hover: rgba(255, 255, 255, 0.65);
  position: relative;
  display: grid;
  grid-template-columns: repeat(8, 1fr);
  grid-template-rows: repeat(8, 1fr);
  width: 100%;
  aspect-ratio: 1;
  container-type: inline-size;
  user-select: none;
  -webkit-user-select: none;
  touch-action: none;
}

.square {
  position: relative;
  background-color: var(--light);
}

.square.dark {
  background-color: var(--dark);
}

.square.selected::before,
.square.last::before {
  content: "";
  position: absolute;
  inset: 0;
  background: var(--highlight);
}

.square.check::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(ellipse at center, rgb(255, 0, 0) 0%, rgb(231, 0, 0) 25%, rgba(169, 0, 0, 0) 89%, rgba(158, 0, 0, 0) 100%);
}

.square.hint::after {
  content: "";
  position: absolute;
  left: 50%;
  top: 50%;
  width: 33%;
  height: 33%;
  transform: translate(-50%, -50%);
  border-radius: 50%;
  background: var(--hint);
  pointer-events: none;
}

.square.hint.capture::after {
  width: 100%;
  height: 100%;
  background: none;
  border: 1.1cqw solid var(--hint);
  box-sizing: border-box;
}

.square.hover {
  box-shadow: inset 0 0 0 0.55cqw var(--hover);
}

.square.movable {
  cursor: grab;
}

.piece {
  position: absolute;
  inset: 0;
  background-repeat: no-repeat;
  background-position: center;
  background-size: 100%;
  pointer-events: none;
  z-index: 1;
}

.piece.hidden {
  visibility: hidden;
}

.drag {
  position: absolute;
  width: 12.5%;
  height: 12.5%;
  left: 0;
  top: 0;
  background-repeat: no-repeat;
  background-position: center;
  background-size: 100%;
  pointer-events: none;
  z-index: 5;
  cursor: grabbing;
}

.board.dragging,
.board.dragging .square.movable {
  cursor: grabbing;
}

.coord {
  position: absolute;
  font-size: 2.3cqw;
  font-weight: 700;
  line-height: 1;
  pointer-events: none;
  z-index: 2;
}

.coord.rank {
  top: 0.55cqw;
  left: 0.55cqw;
}

.coord.file {
  bottom: 0.5cqw;
  right: 0.55cqw;
}

.square.dark .coord {
  color: var(--light);
}

.square.light .coord {
  color: var(--dark);
}

.promotion {
  position: absolute;
  width: 12.5%;
  display: flex;
  flex-direction: column;
  background: #fff;
  box-shadow: 0 0.5cqw 1.5cqw rgba(0, 0, 0, 0.45);
  z-index: 6;
}

.promotion.up {
  flex-direction: column-reverse;
}

.promotion .choice {
  width: 100%;
  aspect-ratio: 1;
  background-repeat: no-repeat;
  background-position: center;
  background-size: 100%;
  cursor: pointer;
}

.promotion .choice:hover {
  background-color: #d9d9d9;
}

.promotion .close {
  width: 100%;
  aspect-ratio: 2;
  background: #f1f1f1;
  color: #666;
  font-size: 2.6cqw;
  line-height: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
}

.promotion .close:hover {
  background: #e4e4e4;
}