If I understand you correctly, I need to add the following (for example) to my skin.xml file in order for the styles set in the skin.css class to take affect?:

<Object>
  <Token>[SOLPARTMENU]</Token>
  <Settings>
   <Setting>
    <Name>menubarcssclass</Name>
    <Value>MainMenu_MenuBar</Value>
   </Setting>
  </Settings>
 </Object>

Thanks for your help Nina!

Dear SFAgitator
Dear dnn-fellows

I can't follow you...
SFAgitator want to setup a vertical sollpartmenu. His question was 'The last thing I'm trying to do is add a 1px solid white border around the main menu cells'.
Perhaps he has find a solution for this question... I don't know. It is the first time that I read this thread.
Then...
The discussion between the dnn-fellows goes over 'how you can see that you've made a change to a menuitem...' And the different answer where very good... but gives not a answer to SFAgitator's question.
Perhaps this can.
The MainMenu_MenuItem is a css class not only for the Menu items on top level but also for the Menu items on submenu level.
If you want different styles then you must set it up. There are no default css class set for special effects.
You must upload this with .xml or directly in your control acsx file of your skin. I've mensioned this also in other threads.

Unfortunately you can not set up border styles at <tr></tr> level... IE and FF doesn't support that.
And this is very important because all the menuclasses that are set on the rootmenu level are set both on <tr></tr> and <td>ROOTMENUITEMNAME</td> level.
Classes that are set at<tr></tr> level support background styles. And with that you can do some styling.
This means for instance MainMenu_MenuItem {border: 1px solid #ff0000;} support only the borders at <td></td> level. When you don't display breadcrumbs or arrows then you can use it...

Another possibility is to use background pictures... but that you know I think. Background pictures are supported on <tr></tr> level.
Hope this will help.