Just put the darker back wall in the background, but leave the player sprite and the playfield at a depth of 0. Don't have anything jutting out of the screen.
The chunky pixels look quite nice, I think :)
Wow, this sucks. Petit computer mk2 was pulled from the eshop a year ago, and the smileboom english site said 'Petit Computer 3 coming in spring 2015!'
:(