View source for your website and CTRL+F for foo.css. wp_enqueue_scripts registers script / style and loads it on your website, it doesn't echo anything.

View source for your website and CTRL+F for foo.css. wp_enqueue_scripts registers script / style and loads it on your website, it doesn't echo anything. Header.php must have wp_head() tag, and footer.php must have wp_footer() tag.