<h6 onmouseover='this.style.background = "orange"'>
  Prueba de concepto
</h6>

const elements = document.querySelectorAll('.hover-background');
elements.forEach(function(item) {
    item.addEventListener('mouseover', function(event) {
        this.style.background = 'orange';
    });
});

<h6 class="hover-background">Prueba de concepto</h6>

.hover-background:hover {
  background: orange;
}

<h6 class="hover-background">Prueba de concepto</h6>