Understanding how the grid works are not only important for determining how to place your widgets but also it helps you determine how to edit the visual appearance of a certain area from the grid.
The layout grid has few levels of depth.
1. The most general and highest level is the page level
2. The second level is the Header, Body and Footer (and Sidebar where applicable)
3. The third and more specific is the row level
4. And the fourth and lowest level is the column level
The Background can be changed on a page level, header, body, footer, sidebar (if applicable) or column and row level. To change the background, you will first need to select the grid level.