If you've ever worked late at night you probably understand the problems with light mode. Your screen is way too bright, and there's a particular strain on your eyes. That is why Microsoft is now adding a dark mode to Word for the Web, helping make it easier for you to focus on your document when the lights are turned out (via Neowin.)
As with most of these incoming features for Microsoft 365 apps, mention of this one is on the Microsoft 365 roadmap. It has the feature ID of 93328 with the appropriate title "Word: Dark Mode." Microsoft doesn't dive into many details, but mentions that it hopes Dark Mode in Word on the web will "provide a modern look for documents while giving users the ability to reduce eye strain and accommodate light sensitivity from long hours at a computer screen."
Other than that, Microsoft says it is targeting a May 2022 release for this dark mode feature. But seeing as though the month of May is now over, we think June could be a better bet. We also aren't sure of how the dark mode might work, but it can be expected to automatically respect your system's light or dark theme, as well as your web browser's settings. A possible toggle switch could also be added under the settings gear, too, but we'll have to wait and see.