<div>W3TR</div>
div {
  background: green;
  width: 200px;
  height: 20px;
  transition: height 2s;
  -webkit-transition: height 2s; /* Safari 3.1 to 6.0 */
  -webkit-transition-delay: 3s; /* Safari */
   transition-delay: 3s;
}
div:hover {
  height: 100px;
}

External CSS

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