I think it makes great sense to have a "Return to default" settings button in customizer section so that whatever changes are made to the cart can be reversed back and default settings can be achieved, I suggest this addition because the user has not fall back option as there is no default customizer.css file loaded during install but it is created after install or first visit to the cart page so if something goes wrong we cannot just cannot upload a new copy of customizer.css file so it is important to have either a "return to default" button(this will basically reset the customizer file to default settings) or have a default customizer.css file uploaded during install. Thank You.