AI Assistant window buttons “Get started”, “Troubleshoot”, “Figma to UI”, “Image to scene” and “Explore” are missing outlines in Light Editor theme

Steps to reproduce:
1. Create new Unity project using Universal 3D Template
2. Make sure Editor theme is set to Light
3. Install AI package via “AI” toolbar button
4. Open Assistant window
5. Observe “Get started”, “Troubleshoot”, “Figma to UI”, “Image to scene” and “Explore” buttons

Actual results: “Get started”, “Troubleshoot”, “Figma to UI”, “Image to scene” and “Explore” buttons are missing outlines

Expected results: “Get started”, “Troubleshoot”, “Figma to UI”, “Image to scene” and “Explore” buttons are not missing outlines (e.g in Dark Editor Theme)

Reproducible with versions: 2.9.0-pre.1 (6000.4.9f1, 6000.5.0b10, 6000.6.0a4)

Tested on (OS): Windows 11, macOS Tahoe 26.4.1 (M1)