@nguyenmv2/buy-button/src/styles/embeds/sass/overrides.css

BuyButton.js allows merchants to build Shopify interfaces into any website

.shopify-buy-frame--product {
  & .shopify-buy__product {
    padding: 0;
  }
}

.shopify-buy-frame--cart {
  & .shopify-buy__quantity {
    border-radius: 0;
    border-left: 0;
    border-left: 0;
    padding: 0;
    font-size: 16px;
  }

  & .shopify-buy__quantity,
  & .shopify-buy__quantity-increment,
  & .shopify-buy__quantity-decrement {
    height: 30px;
  }
}

@media (max-width: 600px) {
  .shopify-buy-frame--modal {
    & .shopify-buy__product {
      width: 100%;
      padding: 30px;
      margin: 0;
    }
  }
}

@media (min-width: 601px) {
  .shopify-buy-frame--modal {
    & .shopify-buy__product {
      width: 100%;
      padding: 45px;
      margin: 0;
    }
  }
}