http://learn.javascript.ru/play/G1ow1
вернет
border: 1px solid red; font-size: 15px; width: 150px; height: 200px;
<!DOCTYPE HTML>
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.js"></script>
<script>
$(document).ready(function(){
$('#div').css('font-size', '15px');
$('#div').css({
width: '150px',
height: 200
})
console.log($('#div').attr('style'))
});
</script>
</head>
<body>
<div id="div" style="border:1px solid red;">dfvdfvdfv</div>
</body>
</html>