Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.2/jquery.min.js"></script>
<script>
$(document).ready(function(){
    $("p:nth-last-child(3n+2)").css("background-color", "yellow");
});
</script>
</head>
<body>

<p>The p:nth-child(3n+2) selects each 3rd paragraph, starting at the last 2nd child element (in this case the eight p element).

<div style="border:1px solid;">
  <p>The first paragraph.</p>
  <p>The second paragraph.</p>
  <p>The third paragraph.</p>
  <p>The fourth paragraph.</p>
  <p>The fifth paragraph.</p>
  <p>The sixth paragraph.</p>
  <p>The seventh paragraph.</p>
  <p>The eight paragraph.</p>
  <span>This is a span element.</span>
</div><br>

</body>
</html>