Gtk-WARNING **: n: Theme parsing error: colors.css:n: Invalid number for color value

I want to share a problem happened to me and I solved it, that when I open an app in the terminal I get that multiline of warning like that:
$ app

(app:2289): Gtk-WARNING **: 08:44:07.973: Theme parsing error: colors.css:71:44: Invalid number for color value

(app:2289): Gtk-WARNING **: 08:44:07.974: Theme parsing error: colors.css:72:44: Invalid number for color value

(app:2289): Gtk-WARNING **: 08:44:07.974: Theme parsing error: colors.css:74:53: Invalid number for color value

(app:2289): Gtk-WARNING **: 08:44:07.974: Theme parsing error: colors.css:75:53: Invalid number for color value

(app:2289): Gtk-WARNING **: 08:44:07.974: Theme parsing error: colors.css:76:56: Invalid number for color value

(app:2289): Gtk-WARNING **: 08:44:07.974: Theme parsing error: colors.css:77:65: Invalid number for color value
I found the solution from that page
https://bugzilla.redhat.com/show_bug.cgi?id=1796781
and worked very well for me.


There is a problem in the default ~/.config/gtk-3.0 At the end, there are following lines:

...
@define-color theme_titlebar_background rgb();
@define-color theme_titlebar_foreground rgb();
@define-color theme_titlebar_background_light #eff0f1;
@define-color theme_titlebar_foreground_backdrop rgb();
@define-color theme_titlebar_background_backdrop rgb();
@define-color theme_titlebar_foreground_insensitive rgb();
@define-color theme_titlebar_foreground_insensitive_backdrop rgb();

Please note the calls to rgb() without arguments.

I have changed these manually to e.g.:

@define-color theme_titlebar_background rgb(71,80,87);
@define-color theme_titlebar_foreground rgb(252,252,252);
@define-color theme_titlebar_background_light #eff0f1;
@define-color theme_titlebar_foreground_backdrop rgb(189,195,199);
@define-color theme_titlebar_background_backdrop rgb(239,240,241);
@define-color theme_titlebar_foreground_insensitive rgb(189,195,199);
@define-color theme_titlebar_foreground_insensitive_backdrop rgb(189,195,199);

and that solved the issue.