How to reproduce:
1. Create a new Unity project
2. Create a UXML file and open it in the UI Builder
3. In the StyleSheets panel, observe the "+" button
Expected results: There is only one "+" on the icon
Actual results: There are two "+" on the icon
Reproducible with: 7000.0.0a11, 7000.0.0a12
Not reproducible with: 7000.0.0a10
Reproducible on: macOS Tahoe 26 (M1)
Not reproducible on: No other environment tested