This project is homework for Nanodegree Front-End Web Developer, Project 2 Animal Trading Cards.
CSS pseudo elements weren't taught yet, but I used one in this project. I used it to keep data clean, such as "25 years" (lifespan of a zebra) versus ": 25 years".
Basic CSS selectors were taught, and they are used here.
The course also pointed us students to further reading for CSS selectors.
Udacity's Nanodegrees are great in that way. Always pushing us to "learn to fish better [for knowledge]". But that could be pretty bad in marketing sense, though, since not many people love to be told to "think for themselves". Still, I guess that works out for Udacity's credentials when partnering with hiring partners (employers looking for good Udacity graduates).