.product-form__buttons button.add-to-cart-button {
  width: 100%;
    max-height: 48px;
    display: block;
    line-height: 0;
    padding: 0;
}

.product-form__buttons button.add-to-cart-button span {
  line-height: 1em;
}

.product-form__buttons .shopify-payment-button {
      width: 100% !important;
}