HTML——JAVASCRIPT——关灯效果

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style type="text/css">
#b
{
    width:%;
    height:%;
    position:fixed;
    top:0px;
    left:0px;
    z-index:;
    background-color:#;
    opacity:0.5;-moz-opacity:0.5;filter:alpha(opacity=);
}
</style>
</head>

<body>
<div id="a" style="z-index:2;position:absolute;height:30px"><input type="button" value="开关" onclick="dianji()"/></div>
<img id="c" src="新建文件夹 (2)/RadArt1_922.jpg"/>
<div id="b" style="display:none"></div>

</body>
<script type="text/javascript">
function dianji()
{
    var s=document.getElementById("b").style.display;
    if(s=="block")
    {
        document.getElementById("b").style.display="none";
    }
    else
    {
        document.getElementById("b").style.display="block";
    }
}

</script>
</html>