How to reduce reduce viewport size and display UMG in place

I am trying to design and inventory screen for my game where when you open the inventory screen it will kind of smush your game to the left and display the inventory on the right. Path of Exile does exactly what I’m talking about and I’m having a lot of trouble finding a function or something to change the viewport in this way in UE4.

Did you ever find an answer to this?

Did anyone?