Theme and editor color scheme not respected

### Involved Module
- [x] UI
- [ ] EvoSuite
- [ ] LLM
- [ ] Kex
- [ ] Other (please explain)

### Describe the bug

If we have a dark "Theme" but a light "editor color scheme", the preview of generated tests mixed up both. The background color follows the "Theme" setting and the text the "editor color scheme" setting. So we have a dark background with a dark text.

The bug also exists with a light "Theme", and a dark "editor color scheme"

### To Reproduce
Steps to reproduce the behavior:
1. Go to Settings -> Appearance
2. Select a dark "Theme" and a light "editor color scheme" (like in the screenshot below)
3. Generate a test with TestSpark
4. In the TestSpark panel, the generated tests preview does not respect "editor color scheme" for the background color.

### Expected behavior

The background color of the generated test preview must follow "editor color scheme" and not "Theme"

### Screenshots
If applicable, add screenshots to help explain your problem.


### Additional context

Reproduce the issue through Settings → Appearance using mismatched Theme and editor color scheme settings, then generate a test and inspect the TestSpark panel's preview. Trace the UI code responsible for the generated test preview and make the background follow the editor color scheme. Done means both dark/light combinations use the editor color scheme consistently.

Written by the indexing model from the issue text.