[BUG] VSCode extension sets <mark> background but not color

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?

Claude's VSCode extension has custom styling for generated plans that it shows the user for review. In these plans the following CSS is set:

mark {
    background: color-mix(in srgb, var(--vscode-editor-findMatchHighlightBackground, #ea5c0055) 60%, transparent);
    border-radius: 2px;
    padding: 1px 0;
    position: relative;
  }

The extension sets the background color of mark elements without changing the foreground color. mark elements are used to highlight text that has been commented on by the user. The foreground color defaults to black, and for users with dark themes the background color will also be black, making the text invisible.

<img width="804" height="367" alt="Image" src="https://github.com/user-attachments/assets/c74a4a37-5732-4db4-8f73-86d1b4c0f129" />

What Should Happen?

The extension should ensure that whatever background is set to, there is enough contrast with the foreground color.

<img width="768" height="352" alt="Image" src="https://github.com/user-attachments/assets/06753f87-7950-44a2-96de-1d432f42e317" />

Error Messages/Logs

N/A

Steps to Reproduce

1. Get Claude to come up with a plan that it opens in a new tab.

1. Set the following color in VSCode's settings to the same as whatever your background color is:

{
    "workbench.colorCustomizations": {
        "editor.findMatchHighlightBackground": "#0000"
    }
}

(as some users use border to highlight matches rather than background)

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.81

Platform

Other

Operating System

Other Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

This has nothing to do with Claude itself, just the VSCode extension.