diff --git a/doccano/app/server/static/forum.css b/doccano/app/server/static/forum.css
index c2d81299..2f2d7d95 100644
--- a/doccano/app/server/static/forum.css
+++ b/doccano/app/server/static/forum.css
@@ -65,10 +65,6 @@ article.post:last-child {
 p {
   font-family: "游ゴシック体", YuGothic, "YuGothic M", sans-serif;
 }
-.box {
-  border-top-left-radius: 0px;
-  border-top-right-radius: 0px;
-}
 .tabs-details {
   margin-right: 1px;
 }