function custom_header_button_script() {

    ?>

    <style>

        #scrolling-button {

            display: none;

        }

    </style>

    <script>

        jQuery(document).ready(function($) {

            $(window).scroll(function() {

                var scroll = $(window).scrollTop();

                if (scroll >= 50) {

                    $("#scrolling-button").fadeIn(200); // fadeIn duration

                } else {

                    $("#scrolling-button").fadeOut(200); // fadeOut duration

                }

            });

        });

    </script>

    <?php

}

add_action('wp_head', 'custom_header_button_script');