I once used Cascadea Safari Extension to change the looks of sites to have darker colors. The extension lets you import any of Stylish themes. Here is a download of all the Cascadea styles I used. For sites I didn't modify with Cascadea, I ran Dark Reader extension which automatically turns all websites dark although with some performance overhead.
I don't use either of those extensions now (due to performance issues + I prefer light themes often for readability during the day). I dream of the future where all sites switch automatically between light & dark themes based of OS theme setting.
Below are some Stylish themes I used:
Hacker News Dark
I prefer reading wiki with Dictionary app as it's fast to search it.
- Awesome Dark Themes for websites
- UserStyles.world - Website to browse and share UserCSS userstyles. (Code)