A couple of months ago, Microsoft Edge Canary enabled a feature which allowed you to automatically match your Light and Dark theme, as selected in the Personalisation section of Windows 10.
Now, in the latest update, you are able to choose a theme directly from the browser’s settings by navigating to:
Settings > Appearance > Theme > Light/Dark/System and adjusting the drop-down there.
Leo Varela kindly provided a quick demonstration of how to do it
Thanks, Leo for the tip.