It looks like you are doing this correctly. When you choose your layout you should edit the css. In the box tab select the outer wrapper, then go into the margin and for the top margin enter the amount and make sure to specify a unit. I set the top margin to 200px and it seemed to work fine for me. Looking at the screen shots it seems that you may have missed the px part, make sure that you select it from the select list after entering the value.