In /usr/share/themes/Radiance/gtk-3.20/apps create the link sudo ln -s gedit.css gnome-builder.css I did not see any difference in gedit, but the error message disappears.
In /usr/share/ themes/ Radiance/ gtk-3.20/ apps create the link
sudo ln -s gedit.css gnome-builder.css
I did not see any difference in gedit, but the error message disappears.