We have a document that addresses the ability to style the new payment experience
https://wpsimplepay.com/doc/how-to-customize-the-payment-method-appearance
The same methods can also be used to adjust the Address field inputs.
The .Input rules can be targeted:
https://stripe.com/docs/elements/appearance-api?platform=web#rules
https://stripe.com/docs/elements/appearance-api?platform=web#form-inputs—labels-above
https://gist.github.com/spencerfinnell/f4b9ccafdbd8ad79cd4a659e7031a8df