How to style caja Desktop background?

If i set theme wise . background wildcard It themes caja background to.Is there a way to exclude caja background (or even better to add a stylish watermark there?)
Kind regards bluedxca93

This code works:

.caja-desktop .background,
.background.caja-desktop-window {
background-image: none;
background-position: right bottom;
background-image: url("assets/beta.png");
background-repeat: no-repeat no-repeat;