dialog's modal set to true doesn't make it a modal without styling applied

dialog's modal set to true doesn't make it a modal without styling applied


here's something I discovered..
if I use the dialog and set model:true but do not use any css styles,
jquery ui will create an overlay div with the proper width/height and
z-index..but won't position it absolutely or relatively.
since z-index only applies to positioned elements...i can still click
on things underneath.
since jquery ui is designed to work even without any styling..is this
an oversight or by design?
david