.to-top {
position: fixed;
display: inline-block;
}
.fst {
position: relative;
z-index: 999;
}
.fst .to-top {
visibility: hidden;
opacity: 0;
transition: opacity 0.3s, visibility 0.3s, background-color 0.3s;
}
.fst .to-top--is-visible {
visibility: visible;
opacity: 1;
}
.fst .to-top:hover {
opacity: 1;
}