css transition

.our_content {
 /* Initially we don't want any height, and we want the contents to be hidden */
 max-height: 0;
 overflow: hidden;

 /* Set our transitions up. */
 -webkit-transition: max-height 0.8s;
 -moz-transition: max-height 0.8s;
 transition: max-height 0.8s;
}
.outside_box:hover .our_content {
 /* On hover, set the max-height to something large. In this case there's an obvious limit. */
 max-height: 200px;
}