Menubar vanished after updating twenty eleven theme

So I updated my wordpress and then the Theme, but after updating the theme (twenty eleven) my menu bar to navigate to the different pages of the website disappeared unfortunately…
I already was a bit playing around with this in my child css to get this menu bar at the bottom of the page, and wanted to adjust it to a pop-up menu.
But i couldnt find my specific problem on the Forum, which i normally use quit much since I am not very well with scripting.

any help is very welcome