[dev-overlay] Blur fader for scrollable container (#77196)
The navigation items overlapping with content looks very bad on scroll:
<img width="289" alt="IMG_9601"
src="https://github.com/user-attachments/assets/85197dc6-eb7e-4919-be59-bc8b2b6a2e5f"
/>
This PR creates a masked fade area that will be visible only when
scrolling:
https://github.com/user-attachments/assets/99757916-8374-4d79-ac2d-762786608f91
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Closes NDX-982
