#header-photos-links {
        background-image: url('museen_FILES/museen-links.jpg');
      }
      
      #header-photos-mitte {
        background-image: url('museen_FILES/museen-mitte.jpg');
      }
      
      #header-photos-rechts {
        background-image: url('museen_FILES/museen-rechts.jpg');
      }