Ah, that’s a different one – it’s not about your theme!
Where have you gotten your domain from?
The problem is that your site does not have an SSL certificate for this domain name therefore it can’t load literally any of the supporting files – scripts, stylesheets, images…
When you add a new domain name to your store you must ensure that there is a SSL certificate matching this name.
Read https://beta-help.shopify.com/en/manual/domains/managing-domains/secure-connections for further info (they mention TLS certificate — it’s the same as SSL cert. in your case).