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<!DOCTYPE html>
<html>
<head>
<style> 
#myDIV {
  width: 300px;
  height: 200px;
  border: 1px solid black;
  animation: mymove 5s infinite;
}
@keyframes mymove {
  50% {border-top: 15px solid lightblue;}
}
</style>
</head>
<body>
<h1>Animation of border-top</h1>
<p>Gradually change the border-top property:<p>
<div id="myDIV"></div>
<p>The border-top is a shorthand property for all border-top properties.</p>
<p>See individual border-top properties to see which is <em>animatable</em>.</p>
</body>
</html>