set dropdown-menu height to 400px

src/client/styles/scss/_on-edit.scss

@@ -315,5 +315,6 @@ body.on-edit {
 
 .bs4grid-menu {
   width: 600px;
-  height: 500px;
+  // [TODO:height adjustment by gw3188]
+  height: 400px;
 }