To make Microsoft Word easier on your eyes, you can enable dark mode by switching the theme to "Black" in the Account menu.

To change the Word page color background from black to white in dark mode, check if you have changed the Windows personalization settings and set it to dark mode.

Microsoft Word's dark mode now inverts the colors of your documents. Previously, the app just inverted the colors of its menus. The change is currently available in the Insiders Beta channel.

Microsoft Word and Google Search are both, separately, getting more extensive dark-mode options to make documents and the web more comfortable to work with at night.