Centered Nested Tabsheet with Scrolling on Resize

I’ve read several similar layout problems, but the solutions don’t seem to help in my case. I have a defined size Panel that contains relative sized components. The Panel is the content of a tabsheet which is the content of a tabsheet which is the content of the main window. The desired effect is much like this forum, but under a tabsheet. I just want the panel to be top-centered in the tabsheet, the tabsheets to fill all available width, and the main window to show scroll bars when resizing below the width/height of the panel dimensions. Any help is much appreciated.