登录按钮在FriendlyChat firebase Web应用程序中不可见

Question

当我尝试在Internet Explorer（11）版本上打开我的友好聊天Firebase网络应用时，Google登录/注销按钮不可见，下面是代码。

 <header class="mdl-layout__header mdl-color-text--white mdl-color--light-blue-700">
    <div class="mdl-cell mdl-cell--12-col mdl-cell--12-col-tablet mdl-grid">
      <div class="mdl-layout__header-row mdl-cell mdl-cell--12-col mdl-cell--12-col-tablet mdl-cell--12-col-desktop">
        <h3><i class="material-icons">chat_bubble_outline</i> FollowMe</h3>
      </div>
      <div id="user-container">
        <div hidden id="user-pic"></div>
        <div hidden id="user-name"></div>
        <button hidden id="sign-out" class="mdl-button mdl-js-button mdl-js-ripple-effect mdl-color-text--white">
          Sign-out
        </button>
        <button hidden id="sign-in" class="mdl-button mdl-js-button mdl-js-ripple-effect mdl-color-text--white">
          <i class="material-icons">account_circle</i>Sign-in with Google
        </button>
      </div>
    </div>
  </header>