smooth scroll css

html {
  scroll-behavior: smooth;
}

/* No support in IE, or Safari
You can use this JS polyfill for those */
http://iamdustan.com/smoothscroll/
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script>
  $(document).ready(function(){
  // Add smooth scrolling to all links
  $("a").on('click', function(event) {
      // Make sure this.hash has a value before overriding default behavior
      if (this.hash !== "") {
      // Prevent default anchor click behavior
        event.preventDefault();
        // Store hash
        var hash = this.hash;
        $('html, body').animate({
          scrollTop: $(hash).offset().top
        }, 800, function(){
          // Add hash (#) to URL when done scrolling (default click behavior)
          window.location.hash = hash;
        });
      } // End if
    });
  });
</script>