1.parent {
2 background: red;
3}
4.child {
5 overflow: hidden;
6 height: 0;
7 background: blue;
8 -webkit-transition: all .8s ease;
9 -moz-transition: all .8s ease;
10 -ms-transition: all .8s ease;
11 -o-transition: all .8s ease;
12 transition: all .8s ease;
13 color: white;
14}
15.parent:hover > .child {
16 height: 30px;
17 display: block;
18}