popup.html

<!DOCTYPE html>
<html>
  <head>
    <link rel="stylesheet" href="resources/bootstrap.min.css"/>
    <link rel="stylesheet" href="resources/style.css"/>
  </head>
  <body>
    <input type="file" id="audio-file-input" class="btn btn-secondary" accept="audio/*,video/*"/>
    <input type="button" id="upload-button" class="btn btn-secondary" value="Upload your file" />
    <div class="preview-wrapper">
      <label>Preview</label>
      <audio controls="true" id="audio" src="" controlsList="nodownload"></audio>
      <div class="section volume-section">
        Volume: <span id="current-volume">100%</span>
      </div>
    </div>
    <div class="footer">
      <button id="save" class="btn btn-primary">Save</button>
      <span id="message"></button>
    </div>
  </body>
  <script src="popup.js"></script>
</html>