JavaScript访问Css

html+js代码：

   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3c.org/TG/xhtml/DTD/xhtml-transitional.dtd">
<html>
<head>
    <title>changeColor.html</title>

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="this is my page">
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">

    <link rel="stylesheet" type="text/css" href="./changeColor.css">
    <script type="text/javascript">
        function changeColor(eventObj){
            //获得css中的所有选择器
            var cssset = document.styleSheets[0].rules;
            //从css中获取所需要的选择器
            var style1=cssset[0];
            if(eventObj.value=="黑色"){
                style1.style.backgroundColor="black";
            }else if(eventObj.value=="红色"){
                style1.style.backgroundColor="red";
            }
        }
    </script>
</head>
<body>
    <div class="style1"></div>
    <input type="button" value="黑色" onclick="changeColor(this);">
    <input type="button" value="红色" onclick="changeColor(this);">
</body>
</html>
css代码：

.style1{
    width: 600px;
    height: 400px;
    background-color: black;
}

补充：web前端 , JavaScript ,