[BUG] Code blocks unreadable in plan mode preview tab on dark themes

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When using plan mode in the VS Code extension, the plan opens in a custom webview tab (with the "Ready for review" banner). Inline code spans and fenced code blocks in this webview render with a light/white background, making text nearly invisible when using a dark editor theme.

What Should Happen?

Code blocks in the plan mode webview should render with colors appropriate for the active editor theme (dark background + light text when using a dark theme).

Error Messages/Logs

Steps to Reproduce

1. Use a dark theme in VS Code/Cursor
2. Enter plan mode (Shift+Tab)
3. Have Claude generate a plan that includes inline code or fenced code blocks
4. The plan opens in a separate tab with the "Ready for review" banner
5. Code blocks render with a light background — text is unreadable

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.77

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Cursor

Additional Information

_No response_