Update Stripe payment checkout to dark theme / custom endpoint

[GodlyDonuts]

The current Stripe payment checkout uses the default white background, which is inconsistent with the dark theme of the rest of the Blade website. This issue is to request changing it to a custom Stripe endpoint or configuring it to match the dark aesthetic of the site.

[myr124]

I believe to customize the stripe screen we need to actually access the branding section in the Stripe dashboard and then we can change colors and theming there.