how to custom the dialog? I don't need the header of dialog...

Hello.
I have a problem with the dialog ui.
I use the dialog as a tooltip in some place,use mouseover and mouseout
to control the dialog,but I found that the header of the dialog is
useless,and I saw all the option no support to remove the header of
the dialog, so can anyone tell me the best way to remove this header?
thank you. forgive my poor englise.