as the icons inside the tool buttons themselves have the same pixel size.
Well, I say "icon size" because we have option ["Icon size"](https://www.geany.org/manual/current/index.html#interface-toolbar-preference...), not "Toolbar size" :)
Just now I don't understand how all it works (for example, why GTK2 support this feature unlike GTK3?), can I will fix it without global change? Or it's not possible?
P.S. For now I returned back on the GTK2-version.