“Contributor” button is a missing border in Light Editor theme

Steps to reproduce:
1. Create new Unity project
2. Make sure Editor Theme is set to Light (Settings > General > Editor Theme > Light)
3. Install Asset Manager package via Package Manager
4. Open Asset Manager Window (Window > Asset Manager)
5. Observe the “Contributor” button 

Actual results: “Contributor” button is a missing border

Expected results: Contributor” button is not missing a border

Reproducible with versions: 1.6.0, 1.7.0 (6000.0.58f1, 6000.2.6f1, 6000.3.0b3, 6000.4.0a1)

Tested on (OS): mac Silicon, Tahoe 26.0 (M1)