Nav Menu (not nestable) with Mega Menu - Menu's in the Mega Menu Template takes style from the top level Menu

Nav Menu (not nestable) with Mega Menu - Menu’s in the Mega Menu Template takes style from the top level Menu.

I am adding menu styles to a class on the Nav Menu,
But it applies to all the sub menus I have in the mega menu template.

Almost one year later and many new versions, still the same behavior. Any chance for some workaround?

Best regards,
Goran