ength} $height ($width) - Hauteur `height` de l’élément
///
/// @example scss - Utilisation
///   .foo
///     +size(10em)
///
///   .bar
///     +size(100%, 10em)
///
/// @example css - CSS après compilation
///   .foo {
///     width: 10em;
///     height: 10em;
///   }
///
///   .bar {
///     width: 100%;
///     height: 10em;
///   }
=size($width, $height: $width)
  width: $width
  height: $height
```
  </div>
</div>
