Use of Ajax HoverMenuExtender as Tooltip

How we can make custom tooltip using Ajax HoverMenuExtender ....

<ajaxControls:HoverMenuExtender ID="HoverMenuExtender1" runat="server" TargetControlID="ImgBtn1" PopupControlID="pnl_Hover_Details" PopupPosition="Right" OffsetX="0" OffsetY="0" PopDelay="0"> </ajaxControls:HoverMenuExtender>

<asp:Panel ID="pnl_Hover_Details" runat="server" Width="150px" Height="50px" BackColor="#CCFF99" BorderColor="#999999" BorderStyle="Solid" BorderWidth="1pt">
  <div style="width: 150px; height: 50px">
      Details are as follow...  </div>
</asp:Panel>