Microsoft Office includes black and dark gray themes. Windows 10’s system-wide dark mode won’t affect Office apps, but you can choose a dark theme for Office apps like Microsoft Word, Excel, Outlook, and PowerPoint.
According to Microsoft, Office’s dark mode is only available if you have a Microsoft 365 (previously known as Office 365) subscription. (However, you can change your theme to “dark gray” on Office 2016 and Office 2013.) This works on any version of Windows, including Windows 7, 8, or 10. The dark themes are currently not available for Office on Mac.