Our beloved is an offspring of the great figure at https://tinyurl.com/temf27hm.
The earlier version is still available:
This is the base jekyll theme as documented at jekyllrb.com, Github Pages and official docs.
The source code for Jekyll is at GitHub: jekyll / jekyll.
The source code for minima is at GitHub: jekyll / minima, e.g., gh-pages-minima-starter and minima-reboot.
The YouTube icon is thankfully from https://icons8.com/icons/set/youtube.