I use the Breeze Dark theme on KDE Neon, which also works perfectly with GTK+2 applications, and I've set GTK+3 programs to use the light theme instead. However, kde-gtk-config only lets me pick a single icon pack for both versions, and my light Breeze GTK+3 applications will use the icon theme made for Breeze Dark. The "fallback theme" option doesn't work for that. I had to edit ~/.config/gtk-3.0/settings.ini manually and set it to read-only to be able to use the light icon theme with it. Please make it possible to use different icon themes for GTK+2 and GTK+3 through the official GUI. Reproducible: Always
I'm not convinced. Why can't we use the same theme for gtk3? what's the use to have a different one?
@Aleix Pol, when you combine a dark GTK+2 theme with a light GTK+3 theme, or vice versa, the icons aren't visible on the latter.
I don't think this is something we'll be doing. Our general direction is improving and increasing the integration between the themes, not pushing them apart. Just use a dark or light theme for all GTK apps; I don't think it makes sense to use different themes for the different versions of GTK.