chess/assets/css/components/_board.scss

@mixin move-indicator {
  border-radius: 50%;
  content: "";
  display: block;
  height: 1.5%;
  position: absolute;
  right: 3%;
  width: 1.5%;
}

.board__container {
  grid-area: board;
}

.board {
  background: $background-color;
  border-collapse: unset;
  border-radius: 2.8%;
  border-spacing: 1px;
  color: $foreground-color;
  height: var(--board-size);
  padding: calc(var(--board-size) / 20);
  position: relative;
  width: var(--board-size);
}

.board--white-to-move,
.board--black-to-move {
  &::before {
    @include move-indicator;
    background: $foreground-color;
  }
}

.board--player-is-white.board--white-to-move,
.board--player-is-black.board--black-to-move {
  &::before {
    bottom: 3%;
  }
}

.board--player-is-white.board--black-to-move,
.board--player-is-black.board--white-to-move {
  &::before {
    top: 3%;
  }
}

.board__rank-labels,
.board__file-labels {
  display: none;
}

.board--player-is-white {
  .board__rank-labels {
    display: flex;
    flex-direction: column-reverse;
  }

  .board__file-labels {
    display: flex;
    flex-direction: row;
  }

  .board__body {
    flex-direction: column-reverse;
  }

  .board__row {
    flex-direction: row;
  }
}

.board--player-is-black {
  .board__rank-labels {
    display: flex;
    flex-direction: column;
  }

  .board__file-labels {
    display: flex;
    flex-direction: row-reverse;
  }

  .board__body {
    flex-direction: column;
  }

  .board__row {
    flex-direction: row-reverse;
  }
}

.board__body {
  background: $background-color;
  border: 0.25rem solid $foreground-color;
  border-radius: calc(var(--board-size) / 100);
  display: flex;
  flex-direction: column;
  height: 100%;
  padding: 1%;
  width: 100%;
}

.board__row {
  display: flex;
  flex-grow: 1;

  @include odd-between(1, 8) {
    .square {
      @include odd-between(1, 8) { @extend %square--black; }
      @include even-between(1, 8) { @extend %square--white; }
    }
  }
  @include even-between(1, 8) {
    .square {
      @include odd-between(1, 8) { @extend %square--white; }
      @include even-between(1, 8) { @extend %square--black; }
    }
  }
}

.board__rank-labels {
  display: none;
  height: 90%;
  left: 0;
  position: absolute;
  width: 5%;
}

.board__file-labels {
  display: none;
  height: 5%;
  position: absolute;
  top: 0;
  width: 90%;
}

.board__label {
  align-items: center;
  display: flex;
  flex-grow: 1;
  font-size: calc(0.25rem + (var(--board-size) / 50));
  justify-content: center;
}

@media (max-aspect-ratio: 9/11) and (max-width: 640px),
       (max-aspect-ratio: 9/11) and (max-height: 640px),
       (min-aspect-ratio: 9/11) and (max-width: 720px),
       (min-aspect-ratio: 9/11) and (max-height: 720px) {
  .board__body {
    border-width: 0.1875rem;
  }
}

@media (max-aspect-ratio: 9/11) and (max-width: 480px),
       (max-aspect-ratio: 9/11) and (max-height: 480px),
       (min-aspect-ratio: 9/11) and (max-width: 560px),
       (min-aspect-ratio: 9/11) and (max-height: 560px) {
  .board__body {
    border-width: 0.125rem;
  }
}

@media (min-width: 480px) {
  .board__body {
    grid-gap: 1px;
  }
}

@media (min-width: 768px) {
  .board__body {
    grid-gap: 2px;
  }
}