In Drupal 7, we can use a template file like page--user--register.tpl.php, or we can register our own template file.
How we can do it in Drupal 8?
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Sign up to join this communityThis is similar in D8. Copy page.html.twig from core or base theme and put it into the template directory of your theme.
Rename it like this:
page--user--register.html.twig