The jPlayer default output uses a lot of CSS to get the player looking respectable. This default set of CSS is based on the demonstration skin provided at http://www.happyworm.com/jquery/jplayer/latest/demos.htm. - THEMING - If you want to override jpalyer.css or jplayer.js place your files under 'your_theme_directory/jplayer/'. ! IMPORTANT ! jplayer.css and jplayer.jpg have to be in the same folder, so if you want to override one of them copy also the other one. Note that the default HTML output of jPlayer module is a standard template that other "skins" may work with. It is highly suggest to not override the jplayer.tpl.php file and instead build all your custom theming on top of the default HTML through CSS.