Sharing my solution to the challenge

const toggleList = document.getElementById('toggleList');
const listDiv = document.querySelector('.list');
const listUl = listDiv.querySelector('ul');

const descriptionP = document.querySelector('p.description');
const descriptionInput =  document.querySelector('input.description')
const descriptionButton = document.querySelector('button.description');

const addItemInput = document.querySelector('input.addItemInput');
const addItemButton = document.querySelector('button.addItemButton');

const lis = listUl.children;

// starts here
function hideEndBtn () {
  listUl.firstElementChild.firstElementChild.style.visibility = 'hidden';
  listUl.lastElementChild.children[1].style.visibility = 'hidden';
}

function showAllBtn () {
  for(let i=0; i<lis.length; i++) {
    for(let j=0; j<lis[0].childElementCount; j++){
      lis[i].children[j].style.visibility = '';
    }
  }
}

function attachListItemButtons (li) {
  let up =document.createElement('button');
  up.className = 'up';
  up.textContent = 'up';
  li.appendChild(up);

  let down =document.createElement('button');
  down.className = 'down';
  down.textContent = 'down';
  li.appendChild(down);

  let remove =document.createElement('button');
  remove.className = 'remove';
  remove.textContent = 'remove';
  li.appendChild(remove);
}

for (let i=0; i<lis.length; i++) {
      attachListItemButtons(lis[i]);
     }
hideEndBtn(); // initially hide the unnecessary button

listUl.addEventListener('click', (event) => {
  if (event.target.tagName=='BUTTON') {
    if (event.target.className == 'remove') {
      let li = event.target.parentNode;
      let ul = li.parentNode;
      ul.removeChild(li);
    }
    if (event.target.className == 'up') {
      let li = event.target.parentNode;
      let prevLi = li.previousElementSibling;
      let ul = li.parentNode;
      if (prevLi) {
        ul.insertBefore(li, prevLi);      
      }
    }
    if (event.target.className == 'down') {
      let li = event.target.parentNode;
      let nextLi = li.nextElementSibling;
      let ul = li.parentNode;
      if (nextLi) {
        ul.insertBefore(nextLi, li);      
      }
    }
    showAllBtn();
    hideEndBtn(); // check whenever move a <li>
  }
});


toggleList.addEventListener('click', () => {
  if (listDiv.style.display == 'none') {
  toggleList.textContent = 'Hide list';  
  listDiv.style.display = 'block';
} else {
  toggleList.textContent = 'Show list';
  listDiv.style.display = 'none';
}
});


descriptionButton.addEventListener('click', () => {
  descriptionP.textContent = descriptionInput.value + ':';
  descriptionInput.value = '';
});

addItemButton.addEventListener('click', () => {
  let ul = document.getElementsByTagName('ul')[0];
  let li = document.createElement('li');
  li.textContent = addItemInput.value;
  attachListItemButtons(li);
  ul.appendChild(li);
  addItemInput.value = '';
  showAllBtn();
  hideEndBtn(); // check whenever add an item
});