MIXINS to create proportional elements // $proportion 4:3 = 75% (3/4*100) // http://www.smashingmagazine.com/2014/02/27/making-embedded-content-work-in-responsive-design/

mixins.sass

=u-proportional-container($proportion: 75%, $boolean: true, $item: item)
  position: relative
  padding-bottom: $proportion
  height: 0
  overflow: hidden
  @if $boolean
    .#{$item}
      position: absolute
      top: 0
      left: 0
      width: 100%
      height: 100%