How do I setup ImageRectOffset?

I've been testing out a bunch of stuff to why my image button won't work. I'm unsure if I might've set up the ImageRectOffset wrong. Any help on how to fix it?

local ImageButton = script.Parent

ImageButton.MouseEnter:connect(function()
ImageButton.ImageRectOffset.unit = Vector2.new(0, 50)
end)

ImageButton.MouseLeave:connect(function()
ImageButton.ImageRectOffset.unit = Vector2.new(0, 0)
end)