Drupal 7 Bartik Menu tabs changed to vertical list - how to reset back to tabs? I have been working on a Drupal 7 install with the Bartik theme.  Today, the main menu tabs changed to a vertical list on the left side of the page.  I do not know how to reset this.  I checked the theme folder and none of the css files have been changed, so I suspect it is either a module I installed today or something I did when I was working on editing some pages.  Any suggestions would be aprpeciated.
Try turning off "Aggregate and compress CSS files" on /admin/config/development/performance and then use right-click inspect element (firefox or chrome) to identify the css responsible for the override. You should see the bartik css files overridden by something else causing this behavior.

A clear cache never hurts either.