Pop-up box background color transparent scroll bar scrolling still centered

popup box div:<Divclass= "WebBox"style="">            <Divclass= "Webboxtop">                <spanclass= "Tstitle">Delivery outlets (receiving outlets)</span>            <ahref="#"class= "CloseBox"></a>            </Div>            <Divclass= "Webboxnr">                <inputtype= "text"class= "Search"ID= "tt"value=""onblur= "This.focus ();"style="">            </Div>        </Div>

Transparent div background <  class= "Zzblack"  style= "Display:block;" ></ Div >

Center Css:.webbox{width:520px;Height:350px;background:#FFFFFF;position:fixed;Z-index:999; Left:50%;Top:50%;Margin-left:-260px;Margin-top:-150px;}. Webboxtop{Height:40px;Line-height:40px;background:#00C049;Padding-left:15px;Color:#FFFFFF;font-size:14px; }. CloseBox{Display:Block;float: Right;width:28px;Height:28px;background:URL (.. /img/close.png) No-repeat;Margin-top:6px;Margin-right:10px;}. Tstitle{float: Left;Display:Block;}. Webboxnr{width:450px;margin:0 Auto;Line-height:30px;Margin-top:20px; }. Search{width:450px;Height:35px;Line-height:35px;Color:#666666;font-size:14px;text-indent:0.5em;Border:1px solid #CCCCCC;Border-radius:5px;}. Zzblack{width:100%;Height:100%;position:Absolute;Top:0; Left:0;background:#888;Opacity:0.5;-webkit-opacity:0.5;-moz-opacity:0.5;Filter:Progid:DXImageTransform.Microsoft.Alpha (opacity=50);}

Pop-up box background color transparent scroll bar scrolling still centered