<html>
<head>
<style>
#myDIV {
width: 300px;
height: 200px;
border: 1px solid black;
animation: mymove 5s infinite;
}
@keyframes mymove {
50% {border-width: 15px;}
}
</style>
</head>
<body>
<h1>Animation of border-width</h1>
<p>Gradually change the border-width property from 1px to 15px, then back:<p>
<div id="myDIV"></div>
</body>
</html>