In the YoutubeFeeder constructor add_action is called for wp_head to run the addHeaderCode() function. This function simply echos the html code to include style.css.
This method means that I cannot apply my own styles - I have to edit the plugin's style.css and these changes will be lost at the next plugin upgrade.
It should use wp_register_style() and wp_enqueue_style() - see the docs at http://codex.wordpress.org/Function_Reference/wp_enqueue_style
This would allow me to call wp_dequeue_style() to exclude the style.css file and use my own styles.