life-cycle-callbacks/index.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Life cycle callbacks test</title>
    <style>
      custom-square {
        margin: 20px;
      }
    </style>
    <script defer src="main.js"></script>
  </head>
  <body>
    <h1>Life cycle callbacks test</h1>

    <div>
      <button class="add">Add custom-square to DOM</button>
      <button class="update">Update attributes</button>
      <button class="remove">Remove custom-square from DOM</button>
    </div>
  </body>
</html>