If you look in the source code of jtable.css it's importing:
@import '../jtable_lightcolor_base.css';
Does the file exist in your directory structure? If not, then that's probably what's causing the issue.
Update
The dialog format is part of jQuery UI and you have not included the jQuery UI CSS
<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.9.0/themes/base/jquery-ui.css" type="text/css" rel="stylesheet" />