options.html

<!DOCTYPE html>
<html>
<head>
<style>
div.container {
    width: 100%;
}

header {
    padding: 10px;
    color: #468847;
    background-color: #dff0d8;
    clear: left;
    text-align: center;
}

nav ul {
    list-style-type: none;
    padding: 0;
}
   
main {
    margin: 0 auto;
	width: 400px;
    padding: 1em;
    overflow: hidden;
}

input {
	width: 350px;
}

button {
	width: 100px;
	margin-left: 140px;
}

</style>
</head>
<body>

<div class="container">

<header>
   <h1>Open in CyberChef Options</h1>
</header>

<main>
  <span>
  URL: <input id="cyberchef_url" type="text" name="cyberchef_url" value="https://gchq.github.io/CyberChef">
  </span>
  <br>
  <br>
  <button id="save">Save</button>
</main>

</div>

<script src="options.js"></script>
</body>
</html>