### Summary The HTML diff for notification email don't apply foreground and background colors consistently. ### Steps to reproduce 1. Create a merge request 2. Add a second participant 3. Have the participant leave a diff comment 4. Use an email client with a dark body background 5. Open the comment notification email ### Example Project https://gitlab.com/gitlab-org/gitlab ### What is the current *bug* behavior? Some diff text is unreadable. Sometimes a custom light background is shown behind default light text, and custom dark text is shown on a default dark background. ### What is the expected *correct* behavior? The `color` CSS attribute on any element that has a custom `background-color` should ensure contrast is preserved and vice versa. ### Relevant logs and/or screenshots Light theme:  Dark theme:  ### Output of checks This bug happens on GitLab.com ### Possible fixes Explicitly define `color` and `background-color` rules together in MR diff emails.