<!DOCTYPE html>
<html>
<head>
  <title>Map test</title>
  <link rel="stylesheet" href="//cdn.leafletjs.com/leaflet-0.7.3/leaflet.css" />
  <!-- If using google basemaps -->
  <!-- <script src="//maps.google.com/maps/api/js?v=3&sensor=false"></script> -->
  <style type="text/css">
  #map {
    height:300px;
    width:100%;
  }
  </style>
</head>
<body>
  <div id="map"></div>
  <div id="key"></div>
  <script type="text/javascript" src="bundle.js"></script>
  <script type="text/javascript" src="config.js"></script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
  <title>Map test</title>
  <link rel="stylesheet" href="//cdn.leafletjs.com/leaflet-0.7.3/leaflet.css" />
  <link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/leaflet.markercluster/0.4.0/MarkerCluster.Default.css" />
  <!-- If using google basemaps -->
  <!-- <script src="//maps.google.com/maps/api/js?v=3&sensor=false"></script> -->
  <style type="text/css">
  #map {
    height:300px;
    width:100%;
  }
  </style>
</head>
<body>
  <div id="map"></div>
  <div id="key"></div>
  <script type="text/javascript" src="bundle.js"></script>
  <script type="text/javascript" src="config.js"></script>
</body>
</html>

Add default cluster styles to example html page
Add default cluster styles to example html page
