ul#myList {
  list-style-type: disc;
  padding-left: 20px;
  margin-top: 10px;
  border: 1px solid #eee;
  padding: 10px;
  min-height: 50px;
}
ul#myList li {
    margin-left: 30px;
}
button#addItemBtn {
  margin-top: 10px;
  padding: 8px 15px;
  cursor: pointer;
}

document.getElementById('addItemBtn').addEventListener('click', function() {
  var list = document.getElementById('myList');
  var newItem = document.createElement('li');
  newItem.textContent = 'New Item ' + (list.children.length + 1);
  list.appendChild(newItem);
});