浮动页面下方层

<style type=text/css>
#master{ margin:0 auto; width:600px;position:absolute; left:100px; top:780px; z-index:999;
 background:#ebd7a2;
 height:28px;
 filter:alpha(opacity=80); /* IE */
 -moz-opacity:0.8; /* Moz FF */
 opacity: 0.8; /* 支持CSS3的浏览器（FF 1.5也支持）*/
}
#master table{ width:600px; text-align:center;}
</style>

<div id="master">

</div>

<script language="JavaScript">
 var oldPosition = 0;
    function flow() {
  var scrollPos;
  var cHeight;

  if (typeof window.pageYOffset != 'undefined') {
     scrollPos = window.pageYOffset;
     cHeight=document.documentElement.clientHeight;
  }
  else if (typeof document.compatMode != 'undefined' &&
    document.compatMode != 'BackCompat') {
     scrollPos = document.documentElement.scrollTop;
     cHeight=document.documentElement.clientHeight;
  }
  else if (typeof document.body != 'undefined') {
     scrollPos = document.body.scrollTop;
     cHeight=document.body.clientHeight;
  }
  var a=scrollPos+cHeight-document.getElementById("master").offsetHeight;
  if(a!=oldPosition){
   document.getElementById("master").style.top = a+'px';
   oldPosition = a;
  }
 }
 window.setInterval("flow()",1);
</script>