Search Icon in the Header Top Bar doesn't work

Hello there, I want to use the WP-Search, but only through the Search Icon in the Header Top Bar, since there is the Theme-Option for that. The Icon appears in the Header Top Bar, but won't react when clicked on and no Searchfield is shown. Only the searchfield in the Header Right Menu is working, but I want to eliminate that from the Page. URL: http://s739007849.online.de/ Thanks in advance! Kind regards, Dirk