ui-dialog css problem

Hello,
I don't know why but theres a border on my dialogs which i couldnt get
rid of.
I deleted all my other css files. Now i have just;
js/ui.core.css
js/ui.dialog.css
js/ui.theme.css
js/ui.datepicker.css
and no change. still have a border on dialog.
I spend my all night to fix this issue but i couldn't :)