The "Night Light" toggle introduced with Windows 10 was an instant hit with users staying up long hours on the PC. When flicked, DWM applies a shader that filters out blue light, and adjusts the color temperature accordingly at a software-level, so even people without monitors that do this can have some degree of protection from the harshness of high color temperature and blue light. The same demographic of people are also looking for an instant toggle that changes Windows to a dark theme. Ask they did, and Microsoft responded in kind, with the Preview Build 17733.

The dark mode can be toggled in the Notifications Center menu of Windows 10. When flicked, all of the areas in Explorer that are normally white, or some brighter shade of gray, turn to black, or a darker shade. Such a UI from Microsoft dates back to the 1990s with its Encarta suite. You can use the dark theme even now, but you'd have to enable it via Windows Settings. It would now take three clicks to bring up the Notifications Center, and toggle both dark mode and night light.