<asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1">

<ProgressTemplate>

    <div class="modal">

        <div class="center">

            <img alt="" src="loader.gif" />

        </div>

    </div>

</ProgressTemplate>

</asp:UpdateProgress>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">

<ContentTemplate>

• PUT YOUR CONTENT HERE LIKE BUTTON , DROPDOWN  ANYTHING THAT YOU WANT

</ContentTemplate>

</asp:UpdatePanel>