EDIT: THANK YOU!!! @AlonGvili nailed it. I needed to add a published folder, then i could set the background locally with
"background" = 'rgba(0, 0, 0, 0) url("/assets/prism.png") repeat scroll 0% 0%'
No, and i just realized that might be the problem. even the asset isn’t served via localhost:80/assets/image.png
I’ll look into Publish-Folder and report.