Change your navigation code by creating HtmlGenericControls instead of adding text to a Literal:

 List<Navigation> theNavigation = DataHelper.GetNavigation();
        theNavigation = theNavigation.OrderBy(u => u.OrderBy).ToList();
 
        foreach (Navigation item in theNavigation)
        {
  HtmlGenericControl li = new HtmlGenericControl("li");
li.ID = item.TabName;
li.Style.Add("display", item.Display);
li.InnerText="><span><a href.......";
......
yourUl.Controls.Add(li);
        }

..and define a UL in your markup to hold the HtmlGenericControls you are creating in code:

<ul runat="server" id="yourUl">
</ul>