Is it possible to select every other group of three in CSS?

Question

Is it possible to select every other group of three in CSS? And if it is; how?

So in the sample below apply style to the 4-6 and 10-12 lis.

Answer 1

You're looking for nth-child:

ul li:nth-child(6n+4),ul li:nth-child(6n+5),ul li:nth-child(6n+6) {
    background:red;
}

http://jsfiddle.net/bhlaird/utEP4/1/