<div>
<span></span>
</div>
<div class='parent'>
<span class='child1'>1</span>
<span class='child2'>2</span>
</div>
.child1 {
display: block;
}
.child2 {
display: none;
}
.parent:hover .child1 {
display: none;
}
.parent:hover .child2 {
display: block;
}