Dear Natalie

I don't know if you've setup these style?...
For instance

<dnn:MENU runat="server"
id="dnnMENU"
menuitemcssclass="RtAndSuMnItNo"
menuitemselcssclass="RtAndSuMnItHo"
rootmenuitemcssclass="RtMnItNo"
rootmenuitemselectedcssclass="RtMnItHo"
rootmenuitemactivecssclass="RtMnItAc"
rootmenuitembreadcrumbcssclass="RtMnItBr"
submenuitemactivecssclass="SuMnItAc"
submenuitemselectedcssclass="SuMnItHo"
submenuitembreadcrumbcssclass="SuMnItBr"
/>

But setting up these styles is not the only thing that you've to to...
All these styles are both set to the <tr></tr> tag and the <td></td> tag.
For instance if you need that the td of the rootmenuitemcssclass have to set, you can use:
.RtMnItNo td {} and define you css class.
Hope this will help.