Markdown diff code block does not color deleted lines in Codex Desktop dark theme

### What version of the Codex App are you using?

Codex Desktop App package: OpenAI.Codex_26.417.5275.0_x64__2p2nqsd0c76g0

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

In Codex Desktop dark theme, Markdown fenced code blocks using the diff language color added lines, but deleted lines are not colored.

The + lines render green, while the - lines render like normal foreground text. This makes deletion lines difficult to distinguish, especially when the removed content itself is Markdown such as bullet lists.

This report is about Markdown diff fenced code blocks rendered inside chat messages. It is not about the dedicated Git diff/review panel.

What steps can reproduce the bug?

Ask Codex to render this Markdown:

~~~markdown

- deleted line
+ added line
-- deleted original Markdown bullet
++ added original Markdown bullet

~~~

What is the expected behavior?

Both diff signs should be visually distinguishable in dark theme:

• + lines should use the added color
• - lines should use a removed/deleted color, for example red

What do you see instead?

• + lines are colored green
• - lines remain near the default foreground color
• Changing theme.semanticColors.diffAdded and theme.semanticColors.diffRemoved through codex-theme-v1 import does not affect Markdown diff code block highlighting, even after restarting the app

Additional information

The dedicated Git diff/review panel does appear to use the configured added/removed colors correctly. This issue is limited to fenced Markdown diff code blocks rendered inside chat messages. Those chat code blocks appear to use syntax-highlighting CSS such as .hljs-addition / .hljs-deletion, rather than theme.semanticColors.diffAdded / theme.semanticColors.diffRemoved.

I inspected the bundled desktop CSS locally. The dark theme appears to define a color for .hljs-addition, but I could not find the corresponding dark-theme .hljs-deletion color rule. I only found .hljs-deletion in the light theme syntax highlight rules.

Potentially related issues:

• #17293
• #18911
• #14187

I have a local screenshot of the reproduction, but gh issue create does not expose a direct local image attachment flag. I can attach it through the GitHub web UI if needed.