How to adjust the constraints for portrait and landscape view?

Question

I have 3 simple buttons, how can I adjust the constraints for portrait and landscape view like below?

Portrait:

Landscape:

Answer 1

I would put these buttons under a stackview and set constraints as below

The Multipler for both height and width is set to 0.8 i.e. 80% of the dimension. And the distribution of stackview to Fill Equally. This would result in :

Portrait

Landscape

With Align center to X & Y of Superview. They will always be centered.