window.addEventListener('load', function() {

    var el = document.querySelector(".sc-classic .tsisartkela-drosha .header__logoLink");
    el.style["background-image"]=url("https://image.flaticon.com/icons/png/512/51/51992.png") //to nie działa
    //el.style["background-image"]=("none") //to działa

}, false);