<html>
<head>
<script src="https://libs.baidu.com/jquery/1.10.2/jquery.min.js">
</script>
<script>
$(document).ready(function(){
$("button").click(function(){
$("div").width(function(n,c){
return c-200;
});
});
});
</script>
</head>
<body>
<button>Decrease width of div with 200 px.</button>
<br><br>
<div style="height:100px;border:4px solid;"></div>
</body>
</html>