Although, if you want to change the Notices color then you can go to Dashboard > Theme Settings > Notices > there you can change the Success and Warning Background and Text Color: https://ibb.co/Jc6QHkd
If you can’t seem to find the one you are looking for then, it means that it is a WooCommerce Notice wrapper. So, for that kindly share that exact Page URL on your Site with us so that we can check and provide you the Custom CSS for that.