Spent a lot of time trying to figure this one out.
When using the Tabs Widget and selecting a tab an outline border would appear on the tab. Tried everything then stumbled across this code:
Cut an paste this to your custom CSS and it will fix the annoyance.
Log into your WordPress Admin. Go to. [Appearance] / [Custom CSS],
and paste in the code above. You will have to clear your cash. But all done no more focus border.
Hope it saved you some time.