I cannot remove a background-image

In my source code there is this entry:

@media (max-width:544px){.ast-separate-container .ast-article-post{background-image:linear-gradient(to right, var(–ast-global-color-5), var(–ast-global-color-5)), url(https://www.liesenfeld.de/WP/wp-content/uploads/back-dark.png);backgrou[…]

I cannot find where I set the background-image in the customizer. I am using the non-pro-version.

• This topic was modified 11 months, 3 weeks ago by dirkliesenfeld. Reason: Found the solution