Custom CSS with knitr and markdown in R

I found this great tutorial on how to modify the css formatting of a HTML report created with markdown and knitr in Rstudio. The post can be found here.

I was hoping to build on this concept and mimic the layout of the page here by using the same css. I tried to simply copy/paste/combine the two css files I found when I viewed the page's source.

Any help you can lend would be greatly appreciated! This is my first attempt and doing anything CSS.