Microsoft's Edge browser has a dark mode... sorta. Thankfully, an honest-to-goodness dark mode is only an extension away -- . Let us review your options for painting Edge black.
Edge's built-in dark theme
Edge has a light and a dark theme. To go dark, click the triple-dot button in the top right of Edge, scroll down and click Settings. On the Settings panel, find Choose a theme and change it from Light to Dark.
The thing is, Edge's theme only touches the row of tabs and URL bar at the top of the window and the favorites, reading list, books, history and downloads panels that slide out from the right. Web pages remain bright white. Bummer.
Turn off the lights
However, you can change that with the Turn Off the Lights extension for Microsoft Edge. Install it and it turns the background of web pages black and the text white. Not by default, though. The extension places a light bulb button in the upper right, but all that does is turn your current web page a dull shade of gray. It's useful when watching YouTube because it fades out everything on the page other than the video player, but useful for little else.
Dig into the extension's options, and you'll find a true dark mode. Click the Night Mode tab in options and then check the box for Show the night switch button below the web page to make the page dark or light. This places a toggle switch in the lower-left corner of Edge to put your current web page in dark mode, complete with a black background and white text.