Ok, I have found the tutorial and downloaded the template. The template relies on an old plugin (Gravatar) which has been replaced by the built-in functionality in WordPress now (I think).
You can update the template by replacing the line in comments.php:
Code:
” alt=”Gravatar” class=”gravatar” />with
Code:
comment_author_email, 40, “https://css-tricks.com/wp-content/themes/CSS-Tricks/images/missing-gravatar.png”); ?>
And in style.css change:
Code:
.gravatar { margin-top: 3px; padding: 2px; height: 40px; }
to
Code:
.avatar { margin-top: 3px; padding: 2px; height: 40px; }