  [ Bonn ] --> [ Berlin ] { shape: circle; }
  [ Bonn ] --> [ Frankfurt ] { background: #deadff; }
  [ Berlin ] ..> [ Cottbus ] { shape: ellipse; }
  [ Berlin ] -> { color: green; } [ Bonn ] { background: #ffdead; }
  [ Cottbus ] -> [ Frankfurt ]
  [ Berlin ] -> [ Ulm ]
  [ Ulm ] -> { color: #a02020; } [ Koblenz]
  [ Ulm ] -> [ Konstanz ] { shape: diamond; }

