You can make every website dark-mode on Chrome by following these instructions:
Open up a Chrome tab
Type "chrome://flags" in the address bar and hit <enter>
Type "dark" in the search bar
Look below for "Auto Dark Mode for Web Content"
There are 5 settings that enable dark mode. I don't know the specific differences, so try each one out and see which one you prefer by going to several sites. My preference so far is "Enabled with simple CIELAB-based inversion" since it seems to leave things like user avatars and pictures alone while still enabling dark mode for the background and text.
Enjoy!
If anyone knows what the different settings mean, please feel free to share, and I will update this post.