简单的div蒙层

#hidediv {
  position:fixed; left:0; top:0; width:100%;  
    height:100%;  background:#000; opacity:0.7; *filter:alpha(opacity=70);
    z-index:1;
    display:none;
    bottom:0;
}

 $("#userLogin").click(function () {
            var heights = (parseInt($(window).height())-200)/2;
            var widths = (parseInt($(window).width())-509)/2;
            $("#waitpay_online").css({ "top": heights + "px", "left": widths + "px" });
            $("#hidediv").slideDown();
            $(".up-box").slideDown();
        })