Please add the code below to your page.
*, *:before, *:after{
-webkit-box-sizing:content-box;
-moz-box-sizing:content-box;
box-sizing:content-box;
}
Or use the newest easyui file, just like this:
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/bootstrap/3.0.2/css/bootstrap.min.css">
<link rel="stylesheet" type="text/css" href="http://www.jeasyui.com/easyui/themes/default/easyui.css">
<link rel="stylesheet" type="text/css" href="http://www.jeasyui.com/easyui/themes/icon.css">
<script type="text/javascript" src="http://www.jeasyui.com/easyui/jquery.min.js"></script>
<script type="text/javascript" src="http://www.jeasyui.com/easyui/jquery.easyui.min.js"></script>
</head>
<body>
<div id="p" class="easyui-panel" style="width:500px;height:200px;padding:10px;"
title="My Panel" iconCls="icon-save" collapsible="true">
The panel content
</div>
</body>
</html>