After Google Chrome, you can now forcibly apply dark mode on websites in Microsoft Edge Canary. Here you should not be confused with Windows 10 dark mode or browser UI theme. Of millions of websites on the internet, only a few sites support dark mode, without needing for the website to support dark mode, you can able to turn every website in Chromium Edge to dark, here is how that can be done.

Force dark theme on websites in Microsoft Edge Chromium
1. Ensure you’re using latest Microsoft Edge Canary 80.0.317.1 or later
2. Visit edge://flags page
3. Search for “dark mod”, for “Force Dark Mode for Web Contents”

4. Select “Enabled” and restart the browser.
Do note there are several options to “automatically render all web contents using a dark theme” in the new Edge browser, but most of them change the website’s background to dark and text to white with slight changes.
Note: To confirm the feature is working or not, set Windows 10 “default App mode” to “Light” and Chromium Edge theme to the system default” or Light” in Appearance Settings.
Related articles:
Microsoft adds High Contrast Mode support to Chrome and Chromium Edge
Chromium Edge: Share button, New Tab Page gets Dark Mode Support
How to Enable Dark Mode in Microsoft Chromium Edge on Windows 10