<script>
  jQuery(function($) {
    $('.trigger-btn').click(function() {
      $('.modal-wrapper').css('display','block');
      $(window).css('background','rgba(0,0,0,0.34)')
      $('.modal-wrapper').addClass('dark-background');
    });

    $('#close-btn').click(function() {
      $('.modal-wrapper').css('display','none');
      $('.modal-wrapper').removeClass('dark-background');
    });

  });
</script>

<style>
  .dark-background{
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    z-index: 9999;
  }
</style>