How to reproduce:
1. Open project "UIToolkit Bug.zip"
2. Open "Test" Scene (Assets>Test)
3. Open UI Toolkit Debugger (Window>UI Toolkit>Debugger)
4. Press on the "Select a panel" button and select "New Panel Settings"
5. Expand VisualElement>TemplateContainer>VisualElement>VisualElement #shop-middle-section>VisualElement #shop-body>ScrollView>VisualElement and select VisualElement #unity-content-viewport
6. In the right window scroll to see "border-top-right-radius"
7. Change value of "border-top-right-radius" or "border-top-left-radius"
8. Look at the Game window

Expected result: Overflow "Hidden" is clipping everything
Actual result: Overflow "Hidden" is not clipping everything

Reproducible with: 2021.2.0b16, 2022.1.0a12
Could not test with: 2019.4.31f1, 2020.3.20f1, 2021.1.25f1 (Errors)