Background doesn't extend far enough on notifications page

[FichteFoll]

All subpages in the notifications hub seem to be affected, specifically also the main one. Happens in native Light or Dark theme.
The background simply stops after what seems to be 100% height of the viewport.

• Browser: FireFox
• Operating System: Arch Linux
• Link to page with the issue: https://github.com/notifications / https://github.com/notifications?query=reason%3Amention
• Screenshot: