fix problem markdown rendered bug

app.css

@@ -168,3 +168,8 @@
   border-right: 1px solid rgba(0, 0, 0, 0.15);
   border-bottom: 1px solid rgba(0, 0, 0, 0.15);
 }
+
+.problem-input-markdown .problem-input-markdown::before {
+  content: "";
+  border: none;
+}