DIV+JS实现半透明效果

function  showSearchResource() ... {

  var iframe=document.getElementById("transbox");
  iframe.style.display="";
  iframe.style.height=document.body.clientHeight;
  window.showModalDialog('searchResource1.html',window,'dialogWidth=690px;dialogHeight=250px;s
                                                        tatus=no');
  iframe.style.display="none";
}

 

< div  id ="transbox"  style ="position:absolute; left:0px; top:0px; display:none;width: 100%;height: 100%;margin: 0 0px;background-color: #000;border: 2px solid black;filter:alpha(opacity=30);opacity: 0.5;-moz-opacity:0.5;" ></ div >