Dear Vlad,
I think I’ve gotten to the bottom of this. It’s a bug in the code, whereby the top menu only receives the background if the promo text has been switched on. To counter this, please go to “Appearance -> Editor” and add the following line at the bottom of “style.css” (should be opened by default):
#nav-primary { float: left; }
My apologies for that, and thanks for pointing it out! I will include the fix in the theme update.
Sincerely,
Andrew | Satori