Style codemirror spelling errors

services/web/public/stylesheets/app/editor/rich-text.less

@@ -219,4 +219,11 @@
     font-style: italic;
     color: #999;
   }
+
+  .spelling-error {
+    background-image: url(/img/spellcheck-underline.png);
+    background-repeat: repeat-x;
+    background-position: bottom;
+  }
 }
+