In Drupal 7, the system.menus.css stylesheet is more-focused version of the Drupal 6 system-menus.css stylesheet. In Drupal 6, it was a difficult stylesheet to override because it included a lot of admin-specific styles.
In Drupal 7, the only admin-specific style is
td.menu-disabled. I think that's a core bug, btw.
If we look at what's left in D7's system-menus.css we find:
- Menu tree styling (Zen has been tweaking this for a long time.)
- Tab styling (Zen has its own.)
- Breadcrumb styling (Zen has its own.)
- Inline link styling (Zen has its own.)
- Active link styling (Zen has a copy in its navigation.css.)
I'm trying to re-do the tab styling (originally written in Zen for Drupal 5) over inand I'm realizing how annoying it is to override all the default tab styling when it would be much simpler to just remove it.