Don't use Cantarell font directly
Here, your app uses
Cantarell font directly:
I use Arch Linux with font changed to Droid Sans in GNOME Tweaks/dconf-editor/gsettings. This way of customization is officially supported by GNOME and GTK.
Please don't do that — instead, make font bigger without specifying font name itself, keeping font which is selected by user in UI. I am not sure but it seems to be you can use