我这段代码为什么不显示
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>操作元素样式</title>
<script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
<link href="style.css" rel="stylesheet" type="text/css" />
</head>
<body>
<h3>css()方法设置元素样式</h3>
<div id="content">我穿了一件红色外衣</div>
<script type="text/javascript">
$("#content").addClass("blue white");
</script>
</body>
</html>
