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 // ===== Scroll to Top ====
    $(window).scroll(function() {
      if ($(this).scrollTop() >= 50) {        // If page is scrolled more than 50px
        $('#return-to-top').fadeIn(200);    // Fade in the arrow
      } else {
        $('#return-to-top').fadeOut(200);   // Else fade out the arrow
      }
    });
    $('#return-to-top').click(function() {      // When arrow is clicked
      $('body,html').animate({
        scrollTop : 0                       // Scroll to top of body
      }, 500);
    });

  <button type="submit" class="scroll-down" id="return-to-top">
    <span>SCROLL</span>
  </button>