NO. Adding dark mode to the compose message window is a very BAD IDEA. Now you have done it, please reverse it ASAP.
Thanks for the feedback! We are working on this.
Current Dark Mode support: https://docs.microsoft.com/en-us/officeupdates/release-notes-office-for-mac
This was a daft idea. We do NOT want the preview pane in dark mode. It looks terrible and makes reading far harder.
The reading pane should not be in dark mode. What are you thinking. Please fix this quickly and at least allow to choose as an option, rather than forcing dark mode on everything in Outlook. Dark mode is intended to allow you to focus on the main window or pane, not to put everything in the dark. MS has got this badly wrong and needs to correct ASAP.