SLS2 responds to the user's device by stacking columns if the screen is narrow. We have four breakpoints - widths at which the screen changes dramatically. The easiest way to think about this is desktop tablet, phone and small phone.
The default for the homepage is left to right; top to bottom; inside to outside. This is industry standard behavior. The default for interior pages is center, right, left; top to bottom; inside to outside. We do this for interior pages so side nav appears at the bottom of the screen in responsive, rather than the middle or top of the page.