A SASS size mixin that allows setting width and height CSS attributes:

@mixin size($width, $height...) {
  @if length($height) == 1 {
    height: $height;
    width: $width;
  } @else {
    height: $width;
    width: $width;
  }
}

It can be used by passing just one argument for both width and height, or 2 separate arguments:

@include size(10px, 20px);
// Compiles to
width: 10px;
height: 20px;

@include size(25px);
// Compiles to
width: 25px;
height: 25px;