Loading spinner next to the generation prompt is poorly visible in the "Light" Unity theme

1. Create a Unity project
2. Set Unity theme to "Light" (Unity -> Settings -> General -> Editor Theme -> Light)
3. Click the "AI" button
4. Click "Agree and install Unity AI"
5. When the installation is complete, open "Assistant"
6. Verify that "Agent" mode would be selected
7. Type any command and observe the result

Actual results: The loading spinner next to the generation prompts is poorly visible

Expected results: The loading spinner next to the generation prompt is clearly visible, with sufficient contrast against the background

Reproducible with versions: 2.0.0-pre.1(6000.5.0a8)

Tested on (OS): macOS - Tahoe 26.3