Question

How, using Nth-Child could I add a class to every red box?

alt text http://www.eirestudio.net/hosting-files/dd.png

I have tried using:

$('#mainnav li ul li:nth-child(3n)').addClass('yes');

Markup:

<ul>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
      <li><a href="">SUUB</a></li>
</ul>

Answer 1

This one will put the yes class on all LIs, except for the first one and then every third:

$('#mainnav li ul li:not(:nth-child(3n+1))').addClass('yes');