You'd want to add a background to the
p-body-header
class. However, that won't include the buttons too because they're part of the
p-body-main
class.
To make it different per node you'd want to do something like this:
CSS:
[data-container-key="node-1"] .p-body-header
{
background: url('//path/to/background/image.jpg') top left no-repeat;
}
You'd change
node-1
to whatever node ID you were wanting to change.