How Does Stripe Generate Such Beautiful Documentation?

I've looked through many documentation packages and have not found anything generating as beautiful as Stripe (e.g., at https://stripe.com/docs/api/metadata). Do they custom-generate this or use a package for it?

Nothing I've researched (e.g., Swagger + various packages, ReadTheDocs) produces something so beautiful.

I know this is silly to say, but I have a sublime experience when interacting with both their website and their documentation. I leave the site happy, soothed, and calmer. I'd like to do this for my own product.