<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'
src='http://code.jquery.com/jquery-2.1.0.js'></script>
<script type='text/javascript'>
$(window).load(function(){
var myvar = 120;
$('#mydiv').css({
width: myvar,
marginLeft: myvar
});
});
</script>
</head>
<body>
<div id="mydiv">test</div>
</body>
</html>