After loading the next article, show its difficulty level in a larger size for one second.

app/templates/userpage_get.html

@@ -204,6 +204,8 @@
         $('#source').html(today_article['source']);
         $('#question').html(today_article["question"]);
         $('#answer').html(today_article["answer"]);
+        $('#text_level').classList.add('display-5'); // enlarge text difficult level for one second
+        setTimeOut(() => {$('#text_level').classList.remove('display-5');}, 1000);
     }
 <!-- 检查是否存在上一篇或下一篇，不存在则对应按钮隐藏-->
     function check_pre(visited_articles){