chess/assets/css/components/_square.scss

%square--black {
  background: repeating-linear-gradient(
    45deg,
    $background-color,
    $background-color ($diagonal-pixel * 5),
    $foreground-color ($diagonal-pixel * 5),
    $foreground-color ($diagonal-pixel * 8)
  );

  &.square--selected {
    box-shadow: inset 0 0 0 0.2rem $foreground-color,
                inset 0 0 0 0.4rem $background-color;
  }

  &.square--available {
    &::after {
      border-radius: 50%;
      bottom: 20%;
      box-shadow: 0 0 0 0.2rem $foreground-color,
                  0 0 0 0.4rem $background-color,
                  inset 0 0 0 0.2rem $background-color;
      content: "";
      display: block;
      left: 20%;
      position: absolute;
      right: 20%;
      top: 20%;
    }
  }
}

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

  &.square--selected {
    box-shadow: inset 0 0 0 0.2rem $foreground-color;
  }

  &.square--available {
    &::after {
      border-radius: 50%;
      bottom: 20%;
      box-shadow: 0 0 0 0.2rem $foreground-color,
                  0 0 0 0.4rem $background-color,
                  inset 0 0 0 0.2rem $background-color;
      content: "";
      display: block;
      left: 20%;
      position: absolute;
      right: 20%;
      top: 20%;
    }
  }
}

.square {
  border-radius: 4%;
  margin: 0.5px;
  position: relative;
  flex-grow: 1;

  // This is to ensure the squares can be clicked on in PhantomJS
  // TODO: Figure out why we need this
  min-height: 20px;
  min-width: 20px;

  &::before {
    background-position: center;
    background-repeat: no-repeat;
    background-size: 100%;
    bottom: 0;
    content: "";
    display: block;
    left: 0;
    position: absolute;
    right: 0;
    top: 0;
  }

  @each $colour in $colours {
    @each $piece in $pieces {
      &.square--#{$colour}.square--#{$piece}::before {
        background-image: url("../static/images/#{$piece}_#{$colour}.svg");
      }
    }
  }
}

@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) {
  %square--black {
    background: repeating-linear-gradient(
      45deg,
      $background-color,
      $background-color ($diagonal-pixel * 3),
      $foreground-color ($diagonal-pixel * 3),
      $foreground-color ($diagonal-pixel * 5)
    );

    &.square--selected {
      box-shadow: inset 0 0 0 0.15rem $foreground-color,
                  inset 0 0 0 0.3rem $background-color;
    }

    &.square--available::after {
      box-shadow: 0 0 0 0.15rem $foreground-color,
                  0 0 0 0.3rem $background-color,
                  inset 0 0 0 0.15rem $background-color;
    }
  }

  %square--white {
    &.square--selected {
      box-shadow: inset 0 0 0 0.15rem $foreground-color;
    }

    &.square--available::after {
      box-shadow: 0 0 0 0.15rem $foreground-color,
                  0 0 0 0.3rem $background-color,
                  inset 0 0 0 0.15rem $background-color;
    }
  }
}

@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) {
  %square--black {
    &.square--selected {
      box-shadow: inset 0 0 0 0.1rem $foreground-color,
                  inset 0 0 0 0.2rem $background-color;
    }

    &.square--available::after {
      box-shadow: 0 0 0 0.1rem $foreground-color,
                  0 0 0 0.2rem $background-color,
                  inset 0 0 0 0.1rem $background-color;
    }
  }

  %square--white {
    &.square--selected {
      box-shadow: inset 0 0 0 0.1rem $foreground-color;
    }

    &.available::after {
      box-shadow: 0 0 0 0.1rem $foreground-color,
                  0 0 0 0.2rem $background-color,
                  inset 0 0 0 0.1rem $background-color;
    }
  }
}