How to highlight ASP.net menu of selected item

Dear All,
I have created ASP.net menu in my ASP.net (Web Form) project. I have one special requirement to highlight main menu as well as selected sub menu which user has clicked but I could not find way to apply CSS of sub menu. This is my sample menu where I want to highlight "Company Management" as well as "Location Information" if user clicked on "Location Information" sub menu. 
<asp:MenuItem Text="Company Management" Value="Company Management" >            <asp:MenuItem Text="Company Information" Value="Company Information"> </asp:MenuItem>            <asp:MenuItem Text="Tax" Value="Tax"></asp:MenuItem>            <asp:MenuItem Text="Location Informat ...