Notifications for PWAs, Webapps

I was too lazy to search through the forums for previous, possible posts on this topic. Feel free to link to the answer if it is out there, or to blame me for my laziness.

Otherwise: is there a way to make a command to enable push notitications/notifications for PWAs or WebApps I made? For the instance I have now, I would like to have my PWA for Fastmail send me notifications when I get a new email. Or, even better, when I have a calendar event upcoming through the Fastmail calendar (this one is probably a stretch).

Any thoughts would be most appreciated.