Summary:
Scrollbar of the new UI (achievements/create a new world) has no bottom limit. The scroll bar can be moved beyond the bottom edge of the gray bar (scroll area). If you move the scrollbar very far off the edge, it will twitch. Also in no other UI does the scrollbar move beyond the bottom edge. It doesn't affect the page, only the scrollbar.

Steps to reproduce:

1. Open "Create new world".
2. Open "Advanced".
3. Use the pointer to move the scroll bar to the very bottom of the screen.

Observed results:
The scroll bar moves beyond the scroll area (gray bar).

Expected results:
The scrollbar will stop when it reaches the bottom of the page.

Screenshots:
Incorrect scrollbar

Correct scrollbar