code: function updateViewportAboveIO() {
      io.viewportAbove = stepEl.map((el, i) => {
        const marginTop = pageH - stepOffsetTop[i];
        const marginBottom = offsetMargin - viewH - stepOffsetHeight[i];
        const rootMargin = `${marginTop}px 0px ${marginBottom}px 0px`;
        const options = { rootMargin };
        // console.log(options);
        const obs = new IntersectionObserver(intersectViewportAbove, options);
        obs.observe(el);
        return obs;
      });
    }
docs: *  OBSERVER - CREATION ** jump into viewport