popup.html

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <style>
        div {
            display: block;
            padding: 5px;
        }
        .setButton {
          background-color: 	rgb(107, 140, 240);
        }
        .removeButton {
          background-color: rgb(236, 148, 174);
        }
    </style>
  </head>
  <body>
      <div>
          <label>间隔(分钟): </label>
          <input id="interval" size="30" value="1"></input>
      </div>
    <div>
        <label>提示文字:&nbsp;&nbsp;</label>
        <input id="tip" size="30" value="休息一下眼睛吧!"></input>
    </div>
    <button id="setRemindButton" class="setButton">设置提醒</button> 
    <button id="removeRemindButton" class="removeButton">取消提醒</button>
    <script src="popup.js"></script>
  </body>
</html>