This bug has been fixed !

I like to have the latest version of WordPress, this is why I use the SVN version. And recently the CSS of the “WP Codebox” plugin stopped working. Here the explanation and the solution :

It seems that starting with the 2.9 version, you can register the styles in the wp_print_scripts action method. So in the wp-codebox.php file, you have to put this :

add_action('wp_print_scripts', 'Codebox_ScriptsAction');
function Codebox_ScriptsAction ()
{
    $cb_path = get_bloginfo('wpurl') . "/wp-content/plugins/wp-codebox"; //URL to the plugin directory
    if (! is_admin()) {
        wp_enqueue_script('jquery');
        wp_enqueue_script('codebox', $cb_path . '/js/codebox.js', array('jquery'), '0.1');
    }
}
 
add_action('wp_print_styles', 'Codebox_StylesAction');
function Codebox_StylesAction() {
        $cb_path = get_bloginfo('wpurl') . "/wp-content/plugins/wp-codebox"; //URL to the plugin directory
        if (! is_admin()) {
                wp_enqueue_style('codebox', $cb_path . '/css/codebox.css', array(), '0.1', 'screen');
        }
}

And it will work.