Scroll animation

   window.addEventListener('scroll', () => {
        let scrollTop = window.scrollY;
        let winHeight = window.document.documentElement.scrollHeight - window.document.documentElement.clientHeight;
        let new_scroll = Math.min(Math.max(scrollTop, 0) / Math.max(winHeight, 1), 1);
        
        document.body.style.setProperty('--scroll', new_scroll);
      }, false);