toggleDropDown.js

<script>
  document.addEventListener('DOMContentLoaded', function() {
    var notificationBtn = document.getElementById('notificationBtn');
    var notificationBox = document.getElementById('notificationBox');

    document.body.addEventListener('click', function(ev) {
      notificationBox.style.display = 'none';
    });

    notificationBtn.addEventListener('click', function(ev) {
      ev.stopPropagation();
      notificationBox.style.display = notificationBox.style.display == 'none' ? 'block' : 'none';
    });
  });
</script>

<button id="notificationBtn">Menu</button>

<div id="notificationBox" style="display: none;">
  <ul>
    <li>...</li>
    <li>...</li>
    <li>...</li>
  </ul>
</div>