A guide on your own domain, such as docs.yourstore.com
A theme guide can now be served at a subdomain you own instead of its /t/ address. On the repository's Theme docs card, under Your own domain, add the subdomain and then the DNS records it lists at your DNS provider; the certificate is issued for you once they're in place, usually within a few minutes, and the card says where the domain stands. While it's active, links to the guide's address here open at the domain, and the password, link previews and keys work as before.
One domain per guide. A bare domain such as yourstore.com works when its DNS is on Cloudflare, which can hold a CNAME at the root; otherwise it's refused and www.yourstore.com suggested. Remove takes the domain off and the guide is read at its address here again. The guide stays unindexed either way.
It's the same custom-domain service Apps use for an app's own domain, so a domain's status, records and certificate are handled the same way in both places.
More in Your own domain.