JavaScript blink essay

<!DOCTYPE html>
<html lang="en">

<head>
  <!-- Global site tag (gtag.js) - Google Analytics -->
  <script async="" src="https://www.googletagmanager.com/gtag/js?id=G-420XFJRS1M"></script>
  <script>
    window.dataLayer = window.dataLayer || [];

    function gtag() {
      dataLayer.push(arguments);
    }
    gtag('js', new Date());
    gtag('config', 'G-420XFJRS1M');
  </script>
  <link rel="shortcut icon" href="https://1xpto.netlify.app/image/favicon.gif" type="image/x-icon">
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>JavaScript blink essay</title>
  <style>
    body {
      margin: 0;
    }

    * {
      box-sizing: border-box;
    }

    #btn {
      outline: 5px solid navy;
      border: 3px solid white;
      border-radius: 50%;
      margin: 50px;
      width: 200px;
      height: 200px;
      background-color: red;
      color: white;
      font-family: arial black;
      font-size: 30px;
    }

    @media (orientation: portrait) {
      #btn {
        margin: 50px auto;
      }
    }
  </style>
</head>

<body>

  <center><button id='btn'>ALERT</button< /center>

      <script>
        delay = 1500;
        setInterval(() => {
          btn.style.opacity = 1;
          setTimeout(() => {
            btn.style.opacity = 0;
          }, delay);
        }, 2000);
      </script>
</body>

</html>