// http://zerosixthree.se/vertical-align-anything-with-just-3-lines-of-css/
// don't forget to put -webkit-transform-style: preserve-3d; on the parent element.
@mixin vertical-align {
  position: relative;
  top: 50%;
  -webkit-transform: translateY(-50%);
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
}