Navigation: sub-menu styles should apply to the sub link only

[madhusudhand]

What problem does this address?

In the current behaviour, a sub-menu is a container with main navigation link + all the sub menu links.
But, the sub menu should only the container of all sub-links, so that the styles applied to the sub-menu doesn't effect the main navigation link.

What is your proposed solution?

Current	expectation

Everything from L1 should always behave as a link.
One of the link might have sub links under it and the container holding all those links should be the sub menu.
Any styling applied to submenu, should get applied to the containing links and container, but not the main nav link itself.

I would like to imagine a scenario where my website has only flat menu first, and then I decide to include nested levels.
In this case I wouldn't expect my main links to get effected by any theme styles, because it is a data change.

However when theme has styles defined for nav-link, that one link having sub-links looks different and it forces me to define styles for submenu to match other navigation links.

Related discussions:

#42963 (comment)