popup.html

<!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title> Extension options </title>
    <link rel="stylesheet" href="/css/popup.css">
    <link href="https://fonts.googleapis.com/css?family=Raleway:300,400" rel="stylesheet">
  </head>
  <body>
    <div id="option-container">
      <h1> What type of background do you like? </h1>
      <p> Example: nature, adventure, .... </p>
      <br>
      <label for="custom-option-label"> enter the type of background </label>
      <br>
      <input type="text" name="custom-option" value="" id="custom-option">
      <br>
      <button type="button" name="option-button" id="option-button"> save </button>
      <br>
      <p id="option-success-message" class="hide-message"></p>
    </div>
  </body>
  <script type="text/javascript" src="js/popup.js"></script>
</html>