https://www.theverge.com/2018/10/30/18042900/microsoft-office-dark-mode-macos-mojave

Microsoft is working on a dark mode option for its Office apps on macOS Mojave. Microsoft Office product manager Akshay Bakshi revealed the new option on Twitter this week, hinting that Office testers will get access to this as soon as next week. The new dark mode for Office will compliment Apple’s general dark mode in macOS Mojave, but it will likely be limited to Office 365 subscribers.

Once testing is finished with Office 365 testers, it will be broadly available for Office users that subscribe to Microsoft’s Office service. While Office 2019 for Mac launched recently, Microsoft is still pushing new features to its Office 365 subscription before any product updates to these standalone licensed apps.