Tutorial: https://www.youtube.com/watch?v=jCglqhIOas8

<script>

// Sent body to overflow hidden on first click of hamburger icon
$('.c-nav_button').click(function() {
  var clicks = $(this).data('clicks');
  if (clicks) {
     $("body").css("overflow", "auto");
  } else {
     $("body").css("overflow", "hidden");
  }
  $(this).data("clicks", !clicks);
});

// Click on the hamburger icon whenever you click on the greyed out part
$( ".c-nav_background" ).click(function() {
  $( ".c-nav_button" ).click();
});

</script>