hi Supriya,
Why don't you make your contents scrollable instead? - Perhaps you can get around without modifying a hell lot of CSS..
Otherwise, you will have to go thru all of the elements controlled by your main UI5 control (possibly the tab control itself and its children) and also apply fixes into the CSS classes to adjust positioning and sizing since I believe you sort of lost the relative layout due the parent property being changed.
Perhaps I can help you out later on with a jsbin or something, what UI5 version are you currently using?
Cheers,
Dan.