Modify style of ‘Pay with Card’ Stripe button

None of those worked for me. I ended up hiding the button in javascript and making a new one.

<form action="/your-server-side-code" method="POST">
    <script src="https://checkout.stripe.com/checkout.js" class="stripe-button"
        data-key="xxx"
        data-amount="999"
        data-name="zzz"         
        data-locale="auto">
    </script>
    <script>
        // Hide default stripe button, be careful there if you
        // have more than 1 button of that class
        document.getElementsByClassName("stripe-button-el")[0].style.display = 'none';
    </script>
    <button type="submit" class="yourCustomClass">Buy my things</button>
</form>