Create a new list item and append it to the DOM – createElement / appendChild

const toggleList = document.getElementById('toggleList');
const listDiv = document.querySelector('.list');
const descriptionInput = document.querySelector('input.description');
const descriptionP = document.querySelector('p.description');
const descriptionButton = document.querySelector('button.description');
const addItemInput = document.querySelector('input.addItemInput');
const addItemButton = document.querySelector('button.addItemButton');
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.innerHTML = descriptionInput.value + ':';
   descriptionInput.value = '';
 });
 addItemButton.addEventListener('click', () => {
   let ul = document.getElementsByTagName('ul')[0];
   let li = document.createElement('li');
   li.textContent = addItemInput.value;
   ul.appendChild(li);
   addItemInput.value = '';
 });