Thank you for the quick reply! These custom css codes work, only it’s placed over all the content. So with a smaller pattern/dots, the text will also be difficult to read. Also, the buttons a.o. won’t work anymore.
It looked like the sorting plugin made changes in the code, outside the plugin as well. So after deactivation, it still effected the theme.
So sorry, it wasn’t a theme issue. Thank you for your help!