<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
div {
width: 150px;
height: 100px;
background: #666;
-webkit-transition-duration: 2s;
-moz-transition-duration: 2s;
-o-transition-duration: 2s;
transition-duration: 2s;
}
div:hover {
width: 600px;
}
</style>
</head>
<body>
<h2>Transition-duration property example</h2>
<div></div>
</body>
</html>