The following line in the "Context Menu" section isn't doing anything:

.context-menu > .separator {
    -fx-padding: 0.0em 0.333333em 0.0em 0.333333em; /* 0 4 0 4 */
}

Because separator isn't a direct child of ".context-menu":
ContextMenu
-> Pane
   -> CSSBridge
      -> ContextMenuContent
         -> MenuBox
            -> Separator

This is especially relevant since developers look up to Modena.css for guidance.