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Source Code:

<!DOCTYPE html>
<html>
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<style>
div {
    background:#00f00f;
    height : 100px;
    width  : 100px;
    position :fixed;
}
</style>
<script src="../../../ajax/libs/jquery/1.10.2/jquery.min.js">
</script>
<script> 
$(document).ready(function(){
  $("button").click(function(){
    $("div").animate({
      width:'300px'
    });
  });
});
</script> 
</head>
<body>
<button>Start Animation</button>
<hr/>
<div></div>
</body>
</html>

Output Preview :

www.c4learn.com/tutorials/ - Try it yourself