"The .app top-level domain is included on the HSTS preload list, making HTTPS required on all connections to .app websites — no individual HSTS registration or configuration required. The result is built-in web security for you and your users." https://get.app/
We use Vercel to deploy our app
We have bought a custom domain
line-height-picker.app
from Google Domains.ns1.vercel-dns.com ns2.vercel-dns.com
, to be deployed to Vercel.To use a custom domain with Vercel, we refer to: https://vercel.com/docs/v2/custom-domains