Everything is closed on Sundays except leisure-related things like restaurants, cinemas, sport venues / gyms and obviously emergency services and the like. It's literally-translated called "Sunday silence". You're also not allowed to make a lot of noise which means stuff like mowing your lawn on Sundays is also not allowed. I never realized how much I appreciated that law until I lived in the Netherlands for a while and had neighbors woodworking loudly on a Sunday. A big exception is Berlin where it's sort of socially accepted to have corner shops (named "Spätis" which means "Laties" as in "being open late") open on Sunday and late at night even though it's technically illegal on a federal level.
It (obviously?) has Christian roots but it is well-ingrained into German society nowadays and is mostly viewed as worker's protection by most people, I would say.