I tried this code from wpbeginner, using SNIPPETS plugin, with with option:
Run snippet everywhere
function wpbeginner_comment_text_before($arg) {
$arg['comment_notes_before'] = "PLEASE NOTE. SHNA board members may or may not respond to posts or comments.";
return $arg;
}
add_filter('comment_form_defaults', 'wpbeginner_comment_text_before');
Did you see my screen capture? That should explain everything.
You can also right-click on the comment box and use the browser inspect tool then check the CSS style. Should be able to see that they are all coming from a plugin.