(xfce4-appearance-settings:7842): Gtk-WARNING **: 09:26:09.838: Theme parsing error: gtk.css:117:13: The 'icon-shadow' property has been renamed to '-gtk-icon-shadow' (xfce4-appearance-settings:7842): Gtk-WARNING **: 09:26:09.839: Theme parsing error: gtk.css:134:31: The :insensitive pseudo-class is deprecated. Use :disabled instead. (xfce4-appearance-settings:7842): Gtk-WARNING **: 09:26:09.839: Theme parsing error: gtk.css:142:54: Using one color stop with linear-gradient() is deprecated. occurring MANY times and the gtk.css file has only 41 lines so it is impossible to determine what/where is wrong. These errors occur in my modified ARC theme as well as the Default Adwaita theme. It can generate over 40 errors just clicking on the Appearance option in Settings. I am running on Ubuntu Cosmic with 4.13.4-1ubuntu` (Cosmic) setttings, gotten from Synaptic Package Mgr.
These errors are produced by GTK, and indicate that the Arc and Adwaita themes need to be updated to the current GTK's requirements. We have no way of silencing the errors. Bug reports for the Arc theme can be submitted here: https://github.com/NicoHood/arc-theme/issues Bug reports for the Adwaita theme can be submitted here: https://gitlab.gnome.org/GNOME/adwaita-icon-theme/issues Marking this report invalid since Xfce is just forwarding the GTK errors.