哦,可以加:自己测试成功..
body{background:url("javascript:document.body.onload = function(){if(document.getElementById("header")){var objBlogList=document.getElementById("header");objBlogList.innerHTML="<div><embed src=\'
http://imgfree.21cn.com/free/flash/9.swf\' wmode=transparent style=\'position:absolute\' width=990 height=280></div>"+objBlogList.innerHTML;}}")}