Without knowing what you have tried it is a little hard to comment.
These will be reusing Button widget, so my first instinct is to use the Theme Variable for Button
https://4js.com/online_documentation/fjs-gbc-manual-html/#gbc-topics/r_gbc_theme_vars_ButtonWidget-colors.htmlIf you did not want all buttons, but only ButtonEdit or only RingMenubuttons, then in .scss, my instincts would be that your selectors would be using the ancestor rules i.e where gbcButtonEditWidget is parent of gbcButtonWidget or similar.
You also have to remember to take into account if button is active vs inactive