I prefer to use dark interfaces on websites. I use Cascadea Safari Extension to change the looks of the sites I use to have darker colors in cases where sites don't have them as default. The extension also lets you import any of Stylish themes to it. Here is a download of all the Cascadea styles I use. For sites that I don't modify with Cascadea, I also run Dark Reader extension which automatically turns all websites dark and does quite a good job at that.
Below are themes I like using:
Although I prefer reading wiki with Dictionary app with its dark mode.