To reproduce:
1. Open the project “Flex End”
2. Select “UIDocument” in the Hierarchy
3. Double click on “MainUI” in the Inspector

Expected result: All buttons are 30% size
Actual result: One button whose margins are set in percentage (bottom row) is expanded

Reproducible with: 2021.3.7f1, 2022.1.11f1, 2022.2.0b3, 2023.1.0a4
Could not test with: 2020.3.38f1 (Package errors)

Reproduced on: macOS Monterey 12.4 (Intel)

Note:
- The CSS file is at Assets → style
- This causes another button in the same row to be out of the container