src: http://zerosixthree.se/vertical-align-anything-with-just-3-lines-of-css/

vertical-center-element.css

.parent-element {
  -webkit-transform-style: preserve-3d;
  transform-style: preserve-3d;
}

.element {
  position: relative;
  top: 50%;
  transform: translateY(-50%);
}

/* Or */
.element {
  position: relative;
  top: 50%;
  transform: perspective(1px) translateY(-50%);
}