Hi Brian,
A very simple example:
1 - Let's say I have a CSS class called DNNHeroHead;
2 - For it to show up on the Editor, create a file called editor.css and add the class DNNHeroHead to it;
3 - Put the file editor.css on the same folder used by your skin;
4 - Make sure you have the same class DNNHeroHead on your skin.css file too so the same style will show outside the editor;
That will do it. I have just tried it myself now.
BTW, make sure you clear your local browser's cache to see this working. This is heavily cached!
Cheers,
Aderson