Steps to reproduce:

1. Create a new Unity project
2. Open the UI Builder window (Window > UI Toolkit > UI Builder)
3. Resize the UI Builder window from the bottom up until Library is no longer visible
4. Observe the UI Builder window

Actual results: It is impossible to access the Library/Hierarchy/Inspector parts, scrolling functionality does not work and a slider does not appear

Expected results: Scrolling functionality works or a slider appears to scroll down and access the Library

Reproducible with versions: 2021.3.50f1, 2022.3.60f1, 6000.0.43f1, 6000.1.0b11, 6000.2.0a7

Tested on (OS): MacOS Silicon Sequoia 15.3

Notes:

• In the Inspector part of the UI Builder window, a slider appears and the scrolling functionality works to access information that does not fit into the window (something has to be selected in the Viewport, for example a VisualElement)
• This is especially a big issue if the user is using UI Builder docked somewhere in the Editor