.to-top {
  display: inline-block;
  height: 40px;
  width: 40px;
  position: fixed;
  bottom: 15px;
  right: 15px;
  background: url(images/back-to-top.png) no-repeat center 50%;
  visibility: hidden;
  opacity: 0;
  z-index: 1000;
}
.to-top.top-is-visible {
  visibility: visible;
  opacity: 1;
}
.to-top.top-fade-out {
  opacity: 0.5;
}
.no-touch .to-top:hover {
  background-color: #33495d;
  opacity: 1;
}