Add darkmode support for difflib's comparison pages

[Wulian233]

Feature or enhancement

Proposal:

Previously, a similar change was made in #123475, which was considered a new feature.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-129939: Add darkmode support for difflib's comparison pages #129940