Although this isn’t covered by theme support, this is one of those things where you will have to try out with the placement of your CSS in the above query group. However, I’m not sure what you want to do when you say more top padding in the far right column you made because when I view it, it looks fine. As for landscape view, this usually is around 650px or less for phones, more for tablets such as the 1024px on high res devices.
By the way, whenever you paste code, highlight it and select the “code” icon on the editor that looks like this
….I just did this to your code.