The code should work fine from the style.css file of the child theme or from Theme Options > Custom css. Please note that from the 4.0 update, all the custom styles come not like inline CSS but as styles from separate file – dynamic.css (to speed up the site loading). If you created child theme before 4.0 update, you need to create the dynamic.css file in woopress-child theme folder and set permissions 777 for the file + add wp_enqueue_style( 'dynamic-css', get_stylesheet_directory_uri() . '/dynamic.css' ); in woopress-child/functions.php file. Then go to Theme Options and re-save them.