options.html

<!DOCTYPE html>
<html>
  <head>
    <style>
      body {
        width: 300px;
        height: auto;
        padding: 10px;
        font-family: Arial, sans-serif;
      }

      input[type='number'] {
        width: 80px;
      }
    </style>
  </head>
  <body>
    <h3>Zoom levels:</h3>
    <p>(If you'd only like to toggle between 2 levels, use -1 as the 3rd level.)</p>
    <form id="zoomForm">
      <label for="zoom1">Zoom 1:</label>
      <input type="number" id="zoom1" min="-1" max="500" required /><br />
      <label for="zoom2">Zoom 2:</label>
      <input type="number" id="zoom2" min="-1" max="500" required /><br />
      <label for="zoom3">Zoom 3:</label>
      <input type="number" id="zoom3" min="-1" max="500" required /><br />
      <button type="submit">Save</button>
    </form>
    <div id="status"></div>
    <script src="options.js"></script>
  </body>
</html>