Scroll bar flickers when opening active packs dropdown

Scroll bar flickers when opening active packs dropdown.

How to reproduce:

1. Enable extra large new UI and disable fullscreen

2. Go to the play screen

3. Go to realms and go to the realm hub of any realm you own

4. Go to worlds

5. Click the active world slot and click the active packs dropdown

6. Observe the scrollbar appearing and disappearing