It looks like it is using the "Tufte" style, named after Edward Tufte, who is very famous for his writing on data visualization. More examples: https://rstudio.

It looks like it is using the "Tufte" style, named after Edward Tufte, who is very famous for his writing on data visualization. More examples: https://rstudio.github.io/tufte/ https://rstudio.github.io/tufte/