Not sure if the responded class is working.

//Remember, list item elements are children of UL elements,
//creating the change event handler.
ul.addEventListener('change', (e) => {
  // console.log(e.target.checked);
  //And now let's get a reference to the
  //check box itself here on the first line of
  const checkbox = event.target;
  //Once we have the value of the checkbox it will be store in checked.
  const checked = checkbox.checked;
  /*
  Now since we'll change the
  class of the list item, when the check box is checked.
  We need a reference to the list item.
  List item is the checkbox is grandparent because
  the label is a child of list item
  So we can traverse to the list item by calling parent node twice
  */
  const listItem = checkbox.parentNode.parentNode;

  //change the class name
  //if true then change class name.
  if (checked) {
    list.className = 'responded';
  } else {
    listItem.className = '';
  }
});