This page has a service worker that is used to send a notification. There's no push involved, all is local.
When you press Request, the app will request permission to show notifications from the browser. If there is no output below, the indicator that the page has requested permission is probably too discrete to see. Look in the address bar for some symbol or text that might indicate this. On Edge it is a bell.
Once you have responded to the request, the result should be shown below. You may now test the notification by pressing Send.
You should see a notification, at different places depending on your device and OS. If you click the notification, a message will appear below.