You need not position the elements you place within your relative containers unless you want a column layout. If you want a horizontal layout, you can place unpositioned elements within containing elements both to position them and to set their content off from the rest of the content.
The inner box is set up as a class here so that you can reuse it; the containing box has been centered, using the auto value. The nested box will be positioned by the normal flow of the content; its width will be determined by the padding in the containing box and its height will be determined by the height of the content.
You need not position the elements you place within your relative containers unless you want a column layout. If you want a horizontal layout, you can place unpositioned elements within containing elements both to position them and to set their content off from the rest of the content.