You’ve now created two DNS records: an A record for yourcustomdomain.com and a CNAME record for www.yourcustomdomain.com. Let’s make sure they both work.
Try opening your website using your root domain in the web browser. You should see your new GitHub Pages site.
Try opening your website using your www subdomain in the web browser. You should see your new GitHub Pages site.
Note: It may take a few minutes for the DNS record to take effect.