gistfile1.html

<script>
  var menu = $('#contact-content');
  
  $('.sidebar #contact-heading').click(function(){
    var heading = $(this);
    
    if ( $(window).width() < 600 ) {
      if( menu.is(':visible') ) {
        menu.slideUp('fast');
        if( heading.hasClass('open') ) {
          heading.removeClass('open');
        }
        heading.addClass('closed');
      } else {
        menu.slideDown('fast');
        if( heading.hasClass('closed') ) {
          heading.removeClass('closed');
        }
        heading.addClass('open');
      }
    }
 });
</script>

<style type="text/css">
  @media screen and (min-width: 600px) {
    #contact-content {
      display: block !important; /* override JS */
    }
  }
  @media screen and (max-width: 599px) {
    #contact-content {
      display: none; /* hide on page load */
    }
  }
</style>