HI larese,
Wow, Feb - I hope you found your answer. But if not - are you looking to put a background on all three elements at once? or each one like the first picture.
If you would like to do them all at once time, I would set a Layout as 1 column and 1 row.
then click inside it and add another layout and add your 3 columns.

On the main layout you did first there should be a "add to Layout" field that stretches under all three nested layouts. click on that and when you see the options - click on Design. Put your background on that layout and it will make the layout work on all 3 nested layouts as if it were one thing.
FYI you won't see the background image until you start putting content into the nested layouts.
hope that helps!
K

Also I was just thinking there is probably a more elegant way to do it in CSS - and put the background image there.
And then add the div to your php file.
But the above mentioned way would by a total "brute force" method to get it done right away.