Calendar notifications shows a Snooze button. But notifications from browsers do not.
Is there any way to enable snooze on Browser's notifications too?
Safari doesn't give you the option to exactly "snooze" website notifications (because the snooze feature is Siri suggested with that notification), but you can manage them:
Perhaps when MacOS Mojave goes public we will see that as an option. If not, feel free to join the beta/development team and petition your request for that feature.
In the mean time these options work best.
You could use Add-on for your Browsers like this one for Chrome