//---------------定义窗口显示位置---------------

function lightboxposition(){
if(document.getElementById("lightbox").style.display=="block")
{
 document.getElementById("lightbox").style.top=(document.documentElement.scrollTop+(document.body.clientHeight-document.getElementById("lightbox").offsetHeight)/2)+"px";
 document.getElementById("lightbox").style.left=(document.documentElement.scrollLeft+(document.body.clientWidth-document.getElementById("lightbox").offsetWidth)/2)+"px";
 }
}