.woocommerce-checkout #payment div.payment_box .form-row.woocommerce-invalid input.input-text,
.woocommerce-checkout #payment div.payment_box .form-row.woocommerce-invalid select{
    border-color: #a00;  
}
.woocommerce-checkout #payment div.payment_box .form-row.woocommerce-validated input.input-text,
.woocommerce-checkout #payment div.payment_box .form-row.woocommerce-validated select{
    border-color: #69bf29;
}