StyleContext variables are not documented
[copied from #25 (comment 79526)]
That's creating big problems for attempts to visually integrate applications which are not using GTK+ toolkit itself but meant to be used on GNU desktop.
A minimal effort to get such spec would be at least to document the StyleContext of Adwaita theme and make that set of variables to be a defined standard.
Discussion covers Awesome WM and Firefox (but the problem also applies to Chromium and, probably, LibreOffice GTK+ frontend and Qt5 GTK StyleProvider).