CSS: centre a child block vertically

centre-vertically.css

/*
*  Centre a child block vertically within its parent.
*  Works in IE9+ and other browsers. http://caniuse.com/#feat=transforms2d
*/
parent {
	position: relative;           /* create a positioning context */
}
child {
	position: absolute;
	top: 50%;                     /* position the top of the element to the middle of the parent */
	transform: translateY(-50%);  /* move the element up by half its height */
}