覆盖整个页面的div

<style type="text/css">
#shadowDiv {
 display: none;
 width: 100%;
 height: 100%;
 position: absolute;
 top: 0px : left : 0px;
 background-color: #FFF;
 filter: alpha(opacity = 70);
 opacity: 0.7;
 z-index: 65534
}
</style>
<script >
window.onload=function test(){
  var d = document.createElement("DIV");
  d.id = "shadowDiv";
  document.body.insertBefore(d, document.body.firstChild);
  d.style.display='block';
  d.style.height=document.body.scrollHeight;
 }
 </script>