That’s not a thing.
But it kinda is!
Bram covers how frustrating .bar:nth-child(2) is. It’s not “select the second element of class .bar.” It’s “select the second element if it also has the class .bar.” The good news? There is a real selector that does the former:
:nth-child(2 of .bar) { }
Safari only. Here are the tickets for Chrome and Firefox.
Direct Link ?