Modal Popup - Ajax toolkit

<ajaxToolkit:ModalPopupExtender ID="MPE" runat="server"
    TargetControlID="LinkButton1"
    PopupControlID="Panel1"
    BackgroundCssClass="modalBackground"
    DropShadow="true"
    OkControlID="OkButton"
    OnOkScript="onOk()"
    CancelControlID="CancelButton"
    PopupDragHandleControlID="Panel3" />