auto resize pannel according to content

I had an pannel which contain the extender modalPopUp.dragcontrol extender and i written css for pannel and model popup

I am using this modelpopUp for multiple forms which contain diffrent contents

i set pannel width and height as 800px and 600 px;

i need auto resize pannel so i can use same css for multiple forms.

--pannel css-------------

.PopUp

{

position:relative;

background-color:#f3f3f8;

border-radius: 7px;

border-right-width:2px;

border-left-width:2px;

border-bottom-width:2px;

border-bottom-style:groove;

border-left-style:groove;

border-right-style:groove;

border-color:#f3f3f8;

width: 800px;

height: 600px;

overflow:auto;

}

---modal popUp-------------------

DynamicServicePath="" Enabled="True" TargetControlID="btnShow"

PopupControlID="pnlPopUp" BackgroundCssClass="backgroundModelPopUp" DropShadow="false"

OkControlID="btnSubmit" CancelControlID="btnclose" >

-----------------------------------