I use Stylish on Safari and Chrome with both the GitHub Dark and Hacker News Dark themes. My eyes couldn't be happier.
https://userstyles.org/styles/37035/github-dark https://userstyles.org/styles/113994/hacker-news-dark
https://userstyles.org/styles/37035/github-dark https://userstyles.org/styles/113994/hacker-news-dark