Reproduction steps:
1. Open the attached “Two Pane Splitter.zip” project
2. Open the “New My Scriptable Object.asset” in the Assets folder
3. Observe the Inspector
Expected results: Borders between the Panes are visible
Actual results: No borders between the Panes are visible
Reproducible with: 2023.2.0a19, 2023.2.6f1, 2023.3.0b3
Not reproducible with: 2021.3.34f1, 2022.3.17f1, 2023.2.0a18
Reproducible on: Windows 11
Not reproducible on: no other environment tested