Steps:
1. Visit https://web-push-book.gauntface.com/demos/notification-examples/
2. Open the web notification

Expected:
Keyboard users should be able to use the download book option in the notification

Notes:
* This is arguably only crucial for screen reader users, but would nonetheless be considered an accessibility violation. 
* Because notifications disappear after a timeout, putting it in the tab order may be helpful but not be ideal, as it may take a while for the user to reach the notification.
* Also because of the auto-disappearance, it's mostly important for interactive notifications (as opposed to needing the keyboard in order to hide the notification).

A multi-pronged solution may be suitable here, e.g.:
- Doable - put it in Tab/F6 order
- Usable for screen reader users - add keyboard shortcut such as Alt+Shift+A and announce in notification contents. Alternative brainstorm idea, if there is an interaction in the notification (rather than just a message), we could automatically focus the notification, at least for screen reader users.