Background of chatbox

Please could someone guide me through changing the background of my chatbox, at present my default forum skin is black, but with a lot of help theme changer was added, but this doesnt carry through to the chatbox (which I have to open in a seperate tab).

I am thinking a grey/pale background would suit most of my members - so if I could get help with this I would be very grateful.

Thanks again..

Thank you will check it out now x