Source code for https://victorfont.com/genesis-html5-go-to-top-source-code/

go_to_top.php

<?php

//* Copy this to the bottom of functions.php
//* Create a shortcode to display our custom Go to top link
add_shortcode('footer_custombacktotop', 'set_footer_custombacktotop');
function set_footer_custombacktotop($atts) {
	return '<a href="#" class="top">Return to top of page</a>';
}

//* Add smooth scrolling for any link having the class of "top"
add_action('wp_footer', 'go_to_top');

function go_to_top() { ?>
	<script>
		jQuery(function($) {
			$('a.top').click(function() {
				$('html, body').animate({scrollTop:0}, 'slow');
			return false;
			});
		});
	</script>
<?php }