WordPress, jQuery UI CSS Files?

Sounds more like you have an issue with finding an available styling within WordPress for the jquery-ui theme.

To answer your question. No, WordPress has no useful styles available within the platform itself. The only available css is in \wp-includes\jquery-ui-dialog.css, and that alone isn’t very useful.

I also had the same issue, and I found two options. Either store it in a CSS folder and load it from there, or load it via URL (Google APIs). For JQuery UI I decided to rely on Google’s CDA and added a way to utilize the ‘Theme Roller’. Storing that amount of css code seems un-nessecary to begin with, and its too bad WordPress doesn’t provide any styling support like they do with the jquery-ui scripts.

However, WP does offer scripts, which will keep the CSS up to date with $wp_scripts->registered['jquery-ui-core']->ver. You can either access it with wp_scripts(); OR global $wp_scripts;.

Static-theme

$wp_scripts = wp_scripts();
wp_enqueue_style('plugin_name-admin-ui-css',
                'http://ajax.googleapis.com/ajax/libs/jqueryui/' . $wp_scripts->registered['jquery-ui-core']->ver . '/themes/smoothness/jquery-ui.css',
                false,
                PLUGIN_VERSION,
                false);

OR Dynamic-theme

$wp_scripts = wp_scripts();
wp_enqueue_style('plugin_name-admin-ui-css',
                'http://ajax.googleapis.com/ajax/libs/jqueryui/' . $wp_scripts->registered['jquery-ui-core']->ver . '/themes/' . $pluginOptions['jquery_ui_theme'] . '/jquery-ui.css',
                false,
                PLUGIN_VERSION,
                false);

And an example of locally storing it

wp_enqueue_style('plugin_name-admin-ui-css',
                plugins_url() . '/plugin-folder-name/includes/css/jquery-ui-theme-name.css',
                false,
                PLUGIN_VERSION,
                false);