Microsoft has already released the Dark mode to the Microsoft Edge browser earlier but that was not available on website contents. It was available to the Microsoft Edge browser only.

Now we have a new flag in Chromium-based Microsoft Edge which is available in Canary that lets you enable dark mode for every webpage. The feature is available in Microsoft Edge Canary 80.0.317.1.
The new flag lets you bring dark mode on websites that do not even support dark mode. It also applies dark mode even where extensions like Dark Reader were not helpful.

How to force dark mode on Edge:

In order to enable the dark mode in Microsoft Edge Canary, you need to type edge://flags and press ‘Enter’ and that will take you to the experimental settings page. Here you can type ‘Dark mode’ and you will get a result showing as ‘Force dark mode for web contents and from there you can enable it. After that, you’ll be prompted to Restart Microsoft Edge Canary. And after the restart, the Edge Canary should have Dark mode everywhere.