JQuery UI and CakePHP

I'm having problem showing JQuery UI themes for my CakePHP application. I placed the theme at app/webroot/lib/jquery.ui/ . Now on my layout I imported the theme using :

echo $html->css('/lib/jquery-ui/theme/ui.all');

I'm usingthe DatePicker widget. On my page, I can see that the my textbox was showing the date picker when focused, but the theme was not applied properly. I can't see the background images. I know that the theme (or css) has been imported since I can see some changes in the DatePicker (fonts, spacings, etc.). I just couldn't see the background images.

I don't know if this has something to do with my problem, but I'm also using YUI.