Use the font variables instead of hardcoding fonts in notes.

app/assets/stylesheets/sections/notes.scss

@@ -76,7 +76,7 @@ ul.notes {
 .diff-file .notes_holder {
   font-size: 13px;
   line-height: 18px;
-  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
+  font-family: $regular_font;
 
   td {
     border: 1px solid #ddd;