Creates a Drupal Ajax 'add_css' command.
This method will add css via ajax in a cross-browser compatible way.
This command is implemented by Drupal.AjaxCommands.prototype.add_css() defined in misc/ajax.js.
$styles: A string that contains the styles to be added.
An array suitable for use with the ajax_render() function.
misc/ajax.js
function ajax_command_add_css($styles) {
return array(
'command' => 'add_css',
'data' => $styles,
);
}