If you’re learning CSS, or you want a friendly introduction to some of its terms and concepts, try 30 Seconds of CSS. Each entry on this site shows a different bit of code, demonstrates the result, and explains how each part of the code works. Here are some entries you’ll understand even if you’re not a designer or developer:
https://lifehacker.com/learn-some-css-30-seconds-at-a-time-1823961025
* second * second * second * second * second * second * LittleSnippets.net