In order to use Dark Mode in Word, Excel, etc, you have to first set the Office Theme to Black. To do this:

1. Open an Office application such as Word or Excel.
2. Click File > Account > Office Theme
3. Set Office Theme to Black.

You can also select “Use System Setting” to have Office use a theme based on your Windows settings for Dark Mode.

Now Dark Mode is turned on, but pages in Word will still appear white.

In order to change the page background to dark do the following:

1. Click View tab in Ribbon.
2. Click Switch Modes button to toggle between dark and light background.

Compatibility

This is tested in Microsoft Office 365 version 2208.