      margin-bottom: 14px;
      }
      #keys table {
        border: 1px solid black;
      }
    </style>
  </head>
  <body>
    <h1>mm.Player with callback</h1>
    <p>An <code>mm.Player</code> also takes an optional <code>CallbackObject</code>, which allows you
      to specify a method to be called after every played note. This is useful
      if you want to sync the audio to a visualization, like below.
    </p>
    <h2>Piano</h2>
    <section>
      <div id='keys'>
        <table cellpadding=0 cells