How to add text separator in submenu?

Hello, I'd like to add a special char as text separator in each submenu(when avaible).
In the attached file you can better understand what I mean.
This char must be not selectable.
What I have to edit?
Thank you

Hi
for me you can just add this in css with a background or border property on the menu items.
CEd

Hello, if I use Border Properties I have the separator also in the last submenu.
What I need is the separator only in the middle, for example 3 voices, 2 separator - 5 voices, 4 separator.

With a background in css should be the same.
There is an hack of maximenu to do this?
thank you

you can add a left border and delete it for the first item :
something like this