Size Mixin DRY

/// Mixin helping defining both `width` and `height` simultaneously.
///
/// @author Hugo Giraudel
///
/// @access public
///
/// @param {Length} $width - Element's `width`
/// @param {Length} $height ($width) - Element's `height`
///
/// @example scss - Usage
/// .foo {
///   @include size(10em);
/// }
///
/// .bar {
///   @include size(100%, 10em);
/// }
///
/// @example css - CSS output
/// .foo {
///   width: 10em;
///   height: 10em;
/// }
///
/// .bar {
///   width: 100%;
///   height: 10em;
/// }
@mixin size($width, $height: $width) {
  width: $width;
  height: $height;
}