Dark mode removes any white background from the web-page, so if you're playing at night, or just want less distracting brightness, playing chess will be easier on your eyes!
To enable it, simply look in the bottom left corner of any page on Chess.com, and click 'Dark UI
This will remove the bright white, and you can enjoy the dark, relaxing background!
If you ever want to switch it back, simply click again, where it will now say Light UI!
See which one you like best!