add class with jquery

include latest jquery file on top.
write code -
<script>
$(document).ready(function(){
    $("#menu-item-2308").addClass("blue");
});
</script>

here menu-item-2308 is id of div where you want to add class and blue is class name.

when using java script use this one

  <script type="text/javascript">
 window.onload = function() {
                document.getElementById('menu-item-134').className = 'blue';
               };
   </script>

Or if you're using jQuery:

$(function() {
  $('#about').addClass('expand');
});