It looks like the author used pandoc with Tufte handout * css: https://github.com/edwardtufte/et-book/ https://github.com/edwardtufte/et-book/ * latex: tufte-

It looks like the author used pandoc with Tufte handout * css: https://github.com/edwardtufte/et-book/ https://github.com/edwardtufte/et-book/ * latex: tufte-handout style from CTAN