jQuery DIV pop-up effect implementation code_jquery

. pop-box {
z-index: 9999; /*This value must be large enough to be displayed on the top*/
margin-bottom: 3px;
display: none;
position: absolute;
background: #FFF;
border:solid 1px #6e8bde;
}

.pop-box h4 {
color: #FFF;
cursor:default ;
height: 18px;
font-size: 14px;
font-weight:bold;
text-align: left;
padding-left: 8px;
padding-top : 4px;
padding-bottom: 2px;
background: url("../images/header_bg.gif") repeat-x 0 0;
}

.pop-box -body {
clear: both;
margin: 4px;
padding: 2px;
}

function popupDiv(div_id) {
var div_obj = $("#" div_id);
var windowWidth = document.documentElement.clientWidth;
var windowHeight = document.documentElement.clientHeight;
var popupHeight = div_obj.height();
var popupWidth = div_obj.width() ;
//Add and display the mask layer
$("").addClass("mask")
.width(windowWidth * 0.99)
.height(windowHeight * 0.99)
.click(function() {hideDiv(div_id); })
.appendTo("body")
.fadeIn(200);
div_obj.css({"position": "absolute"})
.animate({left: windowWidth/2-popupWidth/2,
top: windowHeight/2-popupHeight/2, opacity: "show" }, "slow");
}

function hideDiv(div_id) {
$("#mask").remove();
$("#" div_id).animate ({left: 0, top: 0, opacity: "hide" }, "slow");
}