Here are some customization examples.

CSS

* {
	box-sizing: border-box;
}

body {
	margin: 0;
	padding: 0;
	font-family: Arial, sans-serif;
}

.container {
	max-width: 800px;
	margin: 0 auto;
	padding: 20px;
	text-align: center;
}

h1 {
	margin-top: 0;
}

form input[type="email"] {
	padding: 10px;
	border: none;
	border-radius: 4px;
	margin-right: 10px;
	width: 300px;
}

.btn-join {
	background-color: #4CAF50;
	color: #fff;
	padding: 10px 20px;
	border: none;
	border-radius: 4px;
	font-size: 16px;
	cursor: pointer;
}

.btn-join:hover {
	background-color: #3e8e41;
}

.disclaimer {
	margin-top: 20px;
	font-size: 14px;
	color: #999;
}

HTML

<!DOCTYPE html>
<html>

<head>
  <title>Join Mailing List</title>
  <link rel="stylesheet" href="style.css">
    
  <!-- Add the Google Analytics tracking code here -->
  <script async src="https://www.googletagmanager.com/gtag/js?id=GA_MEASUREMENT_ID"></script>
  <script>
    window.dataLayer = window.dataLayer || [];
    function gtag(){dataLayer.push(arguments);}
    gtag('js', new Date());
    gtag('config', 'GA_MEASUREMENT_ID');
  </script>
</head>

<body>
  <div class="container">
    <h1 id="title">Join Our Mailing List</h1>
    <p>Enter your email address below to receive updates and news:</p>
    <form id="cmForm">
      <input type="email" name="email" placeholder="Enter your email address" id="codemail-email" required>
      <input type="submit" value="Join" class="btn-join">
    </form>
    <p class="disclaimer"></p>
  </div>
  <script src=script.js></script>

  <script type="module">
    import {subscribe, saveCloud} from "https://codemail.zymono.com/1.0/mail.js"
    window.addEventListener("load", function () {
      const cmt = new URLSearchParams(location.search).get('id')
      document.getElementById('cmForm').addEventListener("submit", function (event) {
        event.preventDefault()
        gtag('event', 'subscribe', {
          'event_category': 'Codemail List',
          'event_label': formName,
          'value': 1
        });
        subscribe(cmt, 'Subscribe', './joined/')

      })
    })
  </script>
</body>

</html>

Code © Zymono Codemail. For TESTING use only!