As of 2022-06-08 GitHub is sunsetting the Atom editor.
Giulio Procopio's Atom Retro Syntax Theme
This is essentially vendored from Melina Donati's 90s-tshirt-syntax, however some things didn't sound like they were right. For example, reducing font size of comments causes columns missaligning and preferred line length basically blows up.
You may both use Atom graphical package manager and apm for installation.
apm install https://github.com/giulioprocopio/retro-syntax.gitCheck out also atom.io for installation.