<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <style>
      /* 填写样式 */
    </style>
  </head>

  <body>
    <ul>
      <li>.</li>
      <li>.</li>
      <li>.</li>
    </ul>
    <!-- 填写标签 -->
    <script type="text/javascript">
      // 填写JavaScript
      document.querySelector("ul").onclick = (event) => {
        event.target.innerText += '.';
      };
    </script>
  </body>
</html>