I got it downloaded and imported just fine, and I downloaded the background as well. I set the corkboard preferences to use the new image.
For some reason, the corkboard background works fine on the topmost level of the binder, but when I click the “Outline” folder, it shows the corkboard with a blank background.
Did I miss something?
The corkboard has separate background options for standard, freeform, and label views, so most likely the Outline folder is opening to a different corkboard view than you’ve set up the background image for. You can change the corkboard view mode in the editor footer and the background image either globally in the corkboard appearance preferences. You can also apply an image for the freeform corkboard background just for the specific project in the Background Images pane of the project settings.