6.2.: The menu is hidden after it expands

[Neftalí Espinosa, modificado hace 7 años.]

I have two problems with the navigation menu.
The menu is hidden after expanding and the button has another color, looks dead. It can be seen in the attached gif.

Thanks a lot.

[Byran Zaugg, modificado hace 6 años.]

Many things could be causing this behavior. Could you post the shortest, simplest code needed to reproduce your issue?