ModalPopupExtender Ajax Tool

In Aspx Page

<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Show Popup" />

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </asp:ToolkitScriptManager>
 
    <asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server"
        PopupControlID="Panel1" TargetControlID="Button1">
    </asp:ModalPopupExtender>
    <asp:Panel ID="Panel1" runat="server">
    welcome
        <asp:Button ID="btncancel" runat="server" Text="Button"
            onclick="btncancel_Click" />
    </asp:Panel>

In C#
    protected void Button1_Click(object sender, EventArgs e)
    {
        ModalPopupExtender1.Show();
    }
    protected void btncancel_Click(object sender, EventArgs e)
    {
        ModalPopupExtender1.Hide();
    }