Hook that makes Theme a variation of the theme Base. If Theme does
not define the colours of a class (prolog:console_color/3), those
of Base are used, and so on. The same applies to the styles of the
online help and the theme colours of the development tools. The
theme file of Theme must load the theme file of Base, e.g.
:- module(prolog_theme_my_dark, []).
:- use_module(library(theme/dark)).
:- multifile prolog:theme/1, prolog:theme_base/2.
prolog:theme(my_dark).
prolog:theme_base(my_dark, dark).