Found another solution:
Just add
position: relative;
top: 50%;
transform: translateY(-50%);
to the inner div.
Codepen: http://codepen.io/anon/pen/ZYprdb
Found another solution:
Just add
position: relative;
top: 50%;
transform: translateY(-50%);
to the inner div.
Codepen: http://codepen.io/anon/pen/ZYprdb