def METHOD_NAME(admin_client):
    def post_upload(theme, asset_files=None):
        url = reverse("misago:admin:themes:upload-css", kwargs={"pk": theme.pk})
        if asset_files is not None:
            data = asset_files if isinstance(asset_files, list) else [asset_files]
        else:
            data = ""
        return admin_client.post(url, {"assets": data})
    return post_upload