[BUG] Code block contrast too low in Claude Code web UI (3+ days)

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?

Code blocks in Claude Code web UI have extremely low contrast since ~April 27. Block background is nearly identical to page background, and comment text is barely visible.

<img width="756" height="410" alt="Image" src="https://github.com/user-attachments/assets/daba5b45-3771-4186-a36f-3ec99872e5c2" />

What Should Happen?

Code block background and text should have sufficient contrast to be readable.

Error Messages/Logs

Steps to Reproduce

1. Open Claude Code on the web (claude.ai)
2. View any response containing a code block

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Latest (on the web)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_