Category Module - child arrow back

[tomtolo]

As You can see on the Category Module (left side):
http://ndn.3wstudio.vot.pl/

You can click on arrow and the child categories will go down (nice solution;).
Does anybody know what to do to hide the child categories on another clik on arrow.?


Joomla 2.5.9
VM 2.0.18a