tech support request
@schratze your css would be something like
.cp-app-kanban-container {
background: url(IMAGE_HOSTED_SOMEWHERE) no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
where IMAGE_HOSTED_SOMEWHERE would need to be accessible by that url (don't think you could load anything from local disk there)