// detect scroll direction
        window.scroll_dir = 'down';
        ss_lastScrollTop2 = 0;
        function sej_scroll_dir(){
             let st = Math.round( document.documentElement.scrollTop );   
             if ( st > ss_lastScrollTop2 ){
                 window.scroll_dir = 'down';                   
             } else {
                 window.scroll_dir = 'up';
                
             }
             ss_lastScrollTop2 = Math.round(st);
        }
        window.addEventListener("scroll", sej_scroll_dir );