at the top of the forum you find this link
please use it when you share code and or yaml, it makes reading for other easier, or even possible 
Never mind, I got it going. It turned out that I had to restart appdaemon. I figured that if I restart HA, it will also restart appdaemon, but that did not help. Only when I restart appdaemon the background image changed
Hello,
Can you give me some example of how u get the whole background thing to work ?
I am a beginner.
Thank you so much in advance !
to change a background you need a custom skin:
https://appdaemon.readthedocs.io/en/latest/DASHBOARD_CREATION.html#skin-development
then you need to have the background file on a place where dashboard can find it.
i use /custom_css/images for that.
then you can use that in your css file pointing to /custom_css/images/yourimage.jpg