I created a SButton and placed it on a SOverlay.
SVerticalBox::FSlot& playBtnLaySlot = btnLay->AddSlot();
playBtnLaySlot.AttachWidget(playBtn.ToSharedRef());
playBtnLaySlot.HAlign(EHorizontalAlignment::HAlign_Fill);
playBtnLaySlot.VAlign(EVerticalAlignment::VAlign_Fill);
// This is the important line of code
// viewportRes contains the GameViewport Resolution
// by using GEngine->GameViewport->GetViewportSize(viewportRes);
playBtnLaySlot.Padding(viewportRes.X / 3.0f, 0.0f);
For some reason when I play the game the buttons are placed like this: