@mixin rectangle($width, $height) {
  width: $width;
  height: $height;
}

@mixin round-rectangle($width, $height) {
  @include rectangle($width, $height);

  border-radius: div($height, 2);
}

@mixin square($size) {
  width: $size;
  height: $size;
}

@mixin circle($size) {
  @include square($size);

  border-radius: div($size, 2);
}