As js, they're currently very, er, click-dependent. As hovers, I don't even know at all.
Likely solution:
In T269891#6684977, @Jdlrobson wrote: FYI In Vector and Minerva we use a checkbox hack for the menus. We've been meaning to consolidate the associated CSS code as a core module.
FYI In Vector and Minerva we use a checkbox hack for the menus. We've been meaning to consolidate the associated CSS code as a core module.