In the latest version of this plugin, you call a hook woocommerce_enqueue_stylesand make it call your method/function \Cartflows_Frontend::woo_default_css.
Here you are supposed to add/merge your CSS to the current styles (received in the $woo_styles) parameter. However, you override them with your CSS, making any other CSS inserted before yours unusable, and breaking the checkout css in some cases.
