If you haven't checked it out already, Microsoft has a new all-in-one Office app for Android (and iOS) that kicks the need of having separate apps to handle several file types. After months of user requests, Microsoft is finally rolling out an eye-soothing dark mode for Android.
You can enable the dark mode by tapping on the profile picture at the top right and jumping into settings. Here, you should see a new Display Preferences menu with the option to change the theme. You can manually select the default theme or let the app follow the system theme.
Unfortunately, the dark mode isn't yet quite as universal as we'd like it to be. Although all app elements get the treatment, new documents and spreadsheets miss out on it, making for a pretty jarring experience. It'd be nice to see Microsoft address this in future updates.
If you want to get a taste of the Office in dark mode, make sure to update your application from the Play Store or download it from APK Mirror. Since it's still rolling out, you might have to wait a bit before your app literally joins the dark side.