While I don't know what you mean by "newest" (we are still at module level 1), imho, CSS Tricks has a pretty brief and good cheatsheet. I was able to learn and instantly use flexbox thanks to this guide. While I guess it's not for everyone, I still recommend bookmarking the site, because it can at least be used as a reference later on.
By the way, they also have a similar resource for CSS grid 😉