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I am enjoying the new "snap" applications, but apps installed using this method doesn't seem to be using the system gtk theme I have set.
Some use Adwaita or worse, Raleigh.
How can I have them use the standard Ambience theme I'm using across the whole system?
Snap now has GTK theming support, however it requires to have the same theme installed as a snap which you have chosen on your system.
The official gtk-common-themes snap contains Adwaita, Adwaita-Dark, Ambiance, Arc, Arc-Dark, Arc-Darker, Breeze, Breeze-Dark, Communitheme, elementary, HighContrast, Radiance, and Yaru.
There is also adapta-theme and adapta-gtk-snap as well as gtk2-common-themes for GTK2 apps.
If you're not using one of these themes, I believe you're currently out of luck.
I replaced the snap packages with the apt packages.
I do the following replacement:
sudo snap remove gnome-calculator gnome-characters gnome-system-monitor gnome-logs
sudo apt install gnome-calculator gnome-characters gnome-system-monitor gnome-logs
Now the theme defined in tweak applied to these apps.
In some cases, you can force the snap to start with a theme by using the enviromental variable like this
GTK_THEME=Adwaita-dark /snap/bin/libreoffice.writer
If your theme is not available as a snap, a quick and easy fix is to automatically mount the whole themes folder on top of your snap after reboot. So for example if you're trying to theme Shutter, you would
sudo crontab -e
And add the following line:
@reboot mount --bind -o nodev,ro /usr/share/themes /snap/shutter/current/usr/share/themes
