[javascript] How to change the style of alert box?

_x000D_
_x000D_
<head>_x000D_
  _x000D_
_x000D_
<link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">_x000D_
  <script src="//code.jquery.com/jquery-1.10.2.js"></script>_x000D_
  <script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>_x000D_
  _x000D_
    <script type="text/javascript">_x000D_
  _x000D_
_x000D_
$(function() {_x000D_
    $( "#dialog" ).dialog({_x000D_
      autoOpen: false,_x000D_
      show: {_x000D_
        effect: "blind",_x000D_
        duration: 1000_x000D_
      },_x000D_
      hide: {_x000D_
        effect: "explode",_x000D_
        duration: 1000_x000D_
      }_x000D_
    });_x000D_
 _x000D_
    $( "#opener" ).click(function() {_x000D_
      $( "#dialog" ).dialog( "open" );_x000D_
    });_x000D_
  });_x000D_
    </script>_x000D_
</head>_x000D_
<body>_x000D_
   <div id="dialog" title="Basic dialog">_x000D_
   <p>This is an animated dialog which is useful for displaying information. The dialog window can be moved, resized and closed with the 'x' icon.</p>_x000D_
  </div>_x000D_
 _x000D_
  <button id="opener">Open Dialog</button>_x000D_
_x000D_
</body>
_x000D_
_x000D_
_x000D_