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<!DOCTYPE html>
<html>
<head>
<style>
#myDIV {
  background-color:lightblue;
  width: 100%;
  block-size: 30px;
  animation: mymove 5s infinite;
}
@keyframes mymove {
  50% {block-size: 100px;}
}
</style>
</head>
<body>
<h1>Animation of block-size</h1>
<p>Gradually change the block-size property from 30px to 100px, and back to 30px:<p>
<div id="myDIV">
  This is my DIV element.
</div>
</body>
</html>