[Question]: Custom asset manager background-image in Style Manager

Hello,
i want to use custom Asset Manager
i am used this solution, 
`
var assettarget ='';

    editor.Commands.add('open-assets', {

        run(editor, sender, opts = {})  {

            const modal = editor.Modal;
            const styleManager = editor.styleManager;
            assettarget = opts.target;
            modal.setTitle('Add new image');
            var $test = $("<iframe style='width: 100%; height: calc(100vh - 60px);' src='http://192.168.0.227:45678/weby/fb/filemanager/dialog.php?editor=tinymce&type=1&lang=cs&popup=0&crossdomain=0&relative_url=0&akey=key&fldr=%2F&5ba947c59de97'>test</iframe>");
            $test.on("load", function () {
            
                var iframe = $(this).contents();
                iframe.find('.file').on("click",function(event){
                    var path = $(this).find("img").attr("data-src");
                    path = path.replace("../","./");
                    assettarget.set('src', path);

                });

            })
            
            modal.setContent($test);
            modal.open();
        }
    });

and it works, but now i **am not able to asset background-image in Style Manager**.
It use custom function spreadUrl(), but i dont know how to call it without modify Grapesjs core.
Thanks for help!