attach modalpop with button

<asp:TabContainer ID="TabContainer1" runat="server">
    <asp:TabPanel ID="TabPanel1" runat="server">
      <HeaderTemplate>test tab</HeaderTemplate>
      <ContentTemplate>
        <asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server"
              TargetControlID="Button1"
              PopupControlID="Panel1"
              CancelControlID="CancelButton"
              BackgroundCssClass="testcss"
              Enabled="True" />
        <asp:Button ID="Button1" runat="server" Text="btnpop" />
      </ContentTemplate>
    </asp:TabPanel>
</asp:TabContainer>

<asp:Panel ID="Panel1" runat="server">
    <h1>Popup Panel</h1>
    <asp:Button ID="CancelButton" runat="server" Text="Cancel" />
  </asp:Panel>