<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title></title>
<style type="text/css">
.cls1{
height:200px;
width:300px;
background-color:green;
}
</style>
<script type="text/javascript">
onload = function () {
document.getElementById(‘btn‘).onclick = function () {
document.getElementById(‘dv‘).className = ‘cls1‘;
};
};
</script>
</head>
<body>
<input id="btn" type="button" name="name" value="给div添加样式 " />
<div id="dv"></div>
</body>
</html>
原文：http://www.cnblogs.com/clcloveHuahua/p/5111499.html