Revert "chore: gravatar fallback"

This reverts commit d6df38cb35.

web/app/controllers/subdomain/api/markdown.php

@@ -7,6 +7,10 @@ $purifier_type = UOJRequest::post('purifier_type', 'is_string', 'default');
 
 $markdown = UOJRequest::post('markdown', 'is_string', '');
 
+if ($markdown == '') {
+	$markdown = '_Nothing to preview._';
+}
+
 $parsedown = HTML::parsedown();
 
 if ($purifier_type == 'inline') {

web/app/controllers/subdomain/blog/blog.php

@@ -333,7 +333,7 @@ $comments_pag = new Paginator([
 							</li>
 						</ul>
 						<?php if ($replies) : ?>
-							<div id="replies-<?= $comment['id'] ?>" class="rounded bg-secondary-subtle mt-2 border"></div>
+							<div id="replies-<?= $comment['id'] ?>" class="rounded bg-secondary bg-opacity-10 mt-2 border"></div>
 						<?php endif ?>
 						<script>
 							showCommentReplies('<?= $comment['id'] ?>', <?= $replies_json ?>);

web/app/models/HTML.php

@@ -117,7 +117,7 @@ class HTML {
 			return "https://q1.qlogo.cn/g?b=qq&nk={$user['qq']}&s=$s";
 		}
 
-		return 'https://cravatar.cn/avatar/' . md5(strtolower(trim($user['email']))) . "?d=mm&s=$size";
+		return 'https://cravatar.cn/avatar/' . md5(strtolower(trim($user['email']))) . "?d=404&s=$size";
 	}
 
 	public static function tablist($tabs_info, $cur, $type = 'nav-tabs') {