Is there a list of Gtk4 Style Classes anywhere?

I was looking at the Gtk.Label documentation, and it says:

A wide variety of style classes may be applied to labels, such as .title, .subtitle, .dim-label, etc.

This has me thinking that more style classes than those listed can be applied to labels. I was wondering if there is a list of all the style classes Gtk supports somewhere? I’ve been googling around, but can’t seem to find it.

I think the label classes are documented here: Typography - GNOME Human Interface Guidelines documentation

The most recent libadwaita demo also shows more of them in the “Style Classes” demo.

The list you cited is the most complete documentation we have on this topic. The style classes mentioned there are supported by the themes included in gtk and libadwaita, and I would expect, most other common themes.