Primary nav show as buttons or seperator without CSS?

Is it possible to make the header navigation links show as buttons or at least have a space between them without custom CSS?

I've done quite a bit of searching and I keep arriving at solutions that only involve custom CSS, and nothing that can do it right from within GP Premium. (I also have GP Blocks Pro in case that might be an option, but it doesn't look like there's anything GP Blocks can do with the actual nav menu).

Here are some crudely made images to help convey what I mean...

The standard / default typical GPP nav menu appearance - https://snipboard.io/DW6cAH.jpg

What I would like to have - https://snipboard.io/2M9Cyk.jpg

Or even this would be ok - https://snipboard.io/91EuRK.jpg

The reason I'm hoping for a way to do this without any custom CSS is that I have some clients who will want to be able to make such adjustments after I create their initial layout and most of them are novice when it comes to websites / WP, and they would definitely not like the idea of me having to provide them with custom code & directing them to where to put it would be a less than positive experience. (I'm not design expert myself but copying & pasting some suggested code is not a big deal to me, whereas it is kind of a big deal to clients who want more freedom to experiment from the GUI / editor).

Many thanks for any replies!