Except that native menus don’t really work like that. They have a nontrivial interplay between hovering and mousedown/mouseup that you can’t replicate with just CSS. Not to speak of the missing keyboard functionality.

Native menus? When I need native menus, I use a GUI toolkit, you might have put too much of your concerns into my words.

When I do "native" Menus in HTML I use lists und you can skip to navigation on top if you like but content comes first. And yes, the site works natively in a textmode browser.