CSS Happenings
I started this work as part of the Sovereign Tech Fund initiative, and later on Matthias Clasen joined in and we ended up splitting the work on colors.
Since before GTK switched to CSS for styles, it has had named colors, a non-standard addition providing a similar functionality. You could define a color, then refer to it by name. Unfortunately, they had big limitations. First, they are global. You can only define colors for the whole stylesheet, and if you want to override them for a single widget subtree – you’re out of luck. Second, they were obviously only for colors.
The only option to have them local to a widget was to use gtk_style_context_add_provider() on a GtkStyleContext obtained via gtk_widget_get_style_context. However, it had an even bigger problem: being local to a widget, it didn’t propagate to children, which made it practically useless. Even for widgets that seemingly don’t have children: for example, if you add a provider to a GtkEntry, it won’t affect its text, or the icons, or the progress bar – they are all separate widgets within the entry. So, it shouldn’t be a big surprise that this API is deprecated.
Variables, meanwhile, don’t have any of these limitations. They can be defined anywhere, propagate to children, and they can be anything – colors, numbers, dimensions, etc. For example, we can override them for a specific widget as follows:
