style: Fix source button styles
- Port the style to GTK4 and remove obsolete styles
- Update for libadwaita toolbar margin changes - specifically libadwaita!765 (merged)
Equivalent change in Logs: gnome-logs!57 (merged)
I don't like to make behavior changes, but this one doesn't seem avoidable, and it only affects 2 apps - Calendar and Logs.
Edited by Alice Mikhaylenko