// add a class to the html when the page is scrolled

function add_html_scroll_class(){
    ?>
    <script>
    (function($){
	    $(window).scroll(function() {
            if($(window).scrollTop() > 0) {
			$('html').addClass('html-scrolled');
			$('html').removeClass('html-not-scrolled');
        } else {
			$('html').addClass('html-not-scrolled');
			$('html').removeClass('html-scrolled');
            }
        });
    })(jQuery);
    </script>
    <?php
    }
    add_action('wp_footer', 'add_html_scroll_class');