When I set the background image in CSS I get no result I get this url : localhost/assets/images/karte.svg when I should get such a url: localhost/test.demo/assets/images/karte.svg

By changing which location I get the correct url

 body {
      background-image: url(../../assets/images/karte.svg)
}

Hello,

While I am unsure of your file structure, if you are using a standard/stock Kirby setup and referencing images within…

test.demo/assets/images/karte.svg

…then your CSS URL/file path should be:

background-image: url(../images/karte.svg)