chess/app/styles/main.scss

body {
  background: #124031;
}

$board-square-size: 8vw;
$base-font-size: 16px;

$black-square-color: #824c34;
$white-square-color: #d0bfa1;

$square-outline-color: darken($black-square-color, 20%);

.board {
  display: inline-block;
  font-size: 0;
  border: 0.3vw solid black;
}

.board-square {
  position: relative;
  border: 0.2vw solid $square-outline-color;
  display: inline-block;
  font-size: $base-font-size;
  width: $board-square-size;
  height: $board-square-size;

  img {
    position: absolute;
    margin: 0;
    width: $board-square-size;
  }
}

%black-square {
  background: $black-square-color;  
}

%white-square {
  background: $white-square-color;
}

.board-row:nth-child(odd) {
  .board-square:nth-child(even) {
    @extend %black-square;
  }
  .board-square:nth-child(odd) {
    @extend %white-square;
  }
}

.board-row:nth-child(even) {
  .board-square:nth-child(even) {
    @extend %white-square;
  }
  .board-square:nth-child(odd) {
    @extend %black-square;
  }
}