How to change css class in ajax tabpanel panel at code behind in asp.net

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C#

ASP.NET

Hi friends, i am using ajax tab panel control for tabbing in one of my form.
I have stored the form data in database and manage the status(IsComplete) for each tab form.
At page loading i have checked the tab form status (Iscomplete = true/false) and if it is true then i have to change the css class for that tab.

I have applied css class dynamically from code behind but it is not applying.
My code is :

tbpnl_general.Attributes.Add("class", "ajax__tab_tab complete"); //1st way
tbpnl_general.CssClass = "ajax__tab_tab complete"; //2ed way

but both of code are not applying any class.


My ajax tab panel code is :

<ajax:TabContainer ID="TabContainer1" runat="server" CssClass="fancy fancy-green">

<ajax:TabPanel ID="tbpnl_general" runat="server" Visible="false">
                <HeaderTemplate>
                    Publish
                </HeaderTemplate>
                <ContentTemplate>
                    <asp:Panel ID="pnl_Publish" runat="server">
                        <table width="100%" align="center" style="margin: 50px 0;">
                            <tr>
                                <td>
                                    <asp:LinkButton ID="LiPublished" runat="server" OnClick="LiPublished_Click"><img alt="" src="images/publish.png" /></asp:LinkButton>
                                    <%--<asp:ImageButton ID="LiPublished" runat="server" OnClick="LiPublished_Click" ImageUrl="~/images/publish.png" AlternateText="Publish" />--%>
                                </td>
                            </tr>
                        </table>
                    </asp:Panel>
                </ContentTemplate>
            </ajax:TabPanel>

</ajax:TabContainer>

my css class resides in css file...

Thanks
Sunil Sharma