index.html


<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Heatmaps</title>
    <style>
      html, body, #map-canvas {
        height: 100%;
        margin: 0px;
        padding: 0px
      }
      #panel {
        position: absolute;
        top: 5px;
        left: 50%;
        margin-left: -180px;
        z-index: 5;
        background-color: #fff;
        padding: 5px;
        border: 1px solid #999;
      }
    </style>
    <script src="https://maps.googleapis.com/maps/api/js?v=3.exp&libraries=visualization"></script>
    <script src="https://code.jquery.com/jquery-2.1.1.min.js"></script> 
    <script src="main.js"></script> 
  </head>

  <body>
    <div id="panel">
      <button onclick="toggleHeatmap()">Toggle Heatmap</button>
    </div>
    <div id="map-canvas"></div>
  </body>
</html>