var $menuButton = document.querySelector('.menu-button');
var $sidebar = document.querySelector('.sidebar');
var $contentOverlay = document.querySelector('.content__overlay');

document.addEventListener('DOMContentLoaded', function() {

  $menuButton.addEventListener('click', function() {
    $sidebar.classList.toggle('sidebar--is-visible');
    $contentOverlay.classList.toggle('content__overlay--is-active');
  });

  $contentOverlay.addEventListener('click', function() {
    $sidebar.classList.toggle('sidebar--is-visible');
    $contentOverlay.classList.toggle('content__overlay--is-active');
  });

});