css on body tag in editor

Question

I have a background-image that I apply on the body-tag inside the style.css like this:

body:not(.wp-admin) {
  background: url("…") no-repeat fixed;
  background-size: cover;
}

But it is also shown in the editor where I dont want it. That is what the not-selector is for. I inspected the resulting css in the editor and the rule comes like this:

.editor-styles-wrapper:not(.wp-admin) { … }

How got my styling of the body-tag into the editor-styles wrapper? What is touching my css?