Float/Fixed top menu like in old theme?

Is there a relatively easy way to have the top bar/menu stay fixed and not scroll with the page, like it was in the old atrium theme?

I like pretty much everything in the new theme except this so switching back to the old theme is not an option.

I have played around with CSS overrides but can't seem to get it to work properly, only parts of the menu stay fixed.

Would be awesome with a simple option in the Atrium settings for this, but just a hint how it can be done would be nice.

The CSS is so insanely huge and hairy for the theme...