Hello,
1. Add this code in custom.css file:
.checkout-button.button {
font-size: 15px !important;
}
2. Add the following code in custom.css:
.woocommerce-error, .alert-error, .error {
background-color: #F45B5B !important;
}
Change the color to yours.
Thank you.
Regards,
Eva Kemp.