VS Code extension regression: Codex sidebar/webview background becomes pure black in all themes

### What version of Codex is running?

openai.chatgpt@26.323.20928

### What platform is your computer?

Linux

### What issue are you seeing?

After upgrading the OpenAI Codex VS Code extension to openai.chatgpt@26.323.20928, the Codex sidebar/chat panel
background became pure black.

This happens regardless of the selected VS Code color theme.

The rest of VS Code follows the active theme correctly, but the Codex panel appears to use a fixed black background
instead of matching the theme.

Rolling back to the previous extension version immediately fixes the issue.

### What steps can reproduce the bug?

1. Install or upgrade the VS Code Codex extension to openai.chatgpt@26.323.20928
2. Open the Codex sidebar in VS Code
3. Switch between multiple VS Code themes
4. Observe that the Codex panel background remains pure black in all themes

### What is the expected behavior?

The Codex sidebar should either:

• follow the active VS Code theme, or
• use its own theme consistently without forcing a pure black background across all VS Code themes

### Additional information

• This was not happening in the previous extension version
• Reverting to the previous version fixes the problem
• I checked my VS Code user settings and there were no workbench.colorCustomizations or other custom color overrides

affecting Codex

• This looks like a regression in the extension webview/theme handling