text: 
  const elements = Array.from(document.querySelectorAll('li'));
  
  const callback = entries => {
    console.log(entries);
    entries.
    forEach(entry => entry.
    target.classList.toggle('active', entry.isIntersecting));
  };
  
  const options = {
    treshholds: [
    0, 1] };
  
  
  
  const observers = elements.map(element => {
    const observer = new IntersectionObserver(callback, options);
    observer.observe(element);
    return observer;
  });
  