title: Adding classes to LI with JQuery LI to every 7th item
body: <p>I am using this code to add a class to every 7th LI items and the first one too:</p>
  
  <pre><code>$('ul li:first, ul li:nth-child(7n)').addClass("first"); 
  $('ul li:first, ul li:nth-child(1)').addClass("first"); 
  </code></pre>
  
  <p>My problem is that it just adds the class to the 1st and the 7th item but if I add another 7 or more it doesn't add it.</p>
  
  <p>I need to add the class the every 7th li item.</p>