JSFiddle - React, Tailwind, and code Playground

HTML

<span id="tlacitko" onmouseover="f();" onmouseout="f();">Najeď na mě</span>

JavaScript

function zmen(element,src1,src2) {
    element.style.backgroundImage = (element.style.backgroundImage == 'url("' + src1 + '")' ? 'url("' + src2 + '")' : 'url("' + src1 + '")');
}

var f = function() {zmen(document.body,'https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTmJSpnBxTXO3LdJ25f5fVvUDQjTr2H1Ic3i4dULBLc_aKTRdOX','http://upload.wikimedia.org/wikipedia/commons/7/73/Love_math_1.jpg')};