.back-to-top {
  background: #fff;
  display: block;
  text-align: center;
  width: 44px;
  line-height: 44px;
  border-radius: 27px;
  box-shadow: 0 0 4px rgba(0,0,0,.5);
  opacity: 1;
  transition: opacity .5s;
}

.back-to-top:hover {
  text-decoration: none;
}

.back-to-top.back-to-top--sticky {
  position: fixed;
  bottom: 0;
  right: 0;
  margin: 16px 3.75%;
}

@media (max-width:650px) {
  .back-to-top.back-to-top--sticky {
    margin: 16px;
  }
}

@media (min-width:651px) and (max-width:999px) {
  .back-to-top.back-to-top--sticky {
    margin: 16px 3.4375%;
  }
}

.back-to-top.back-to-top--unnecessary {
  opacity: 0;
  pointer-events: none;
}

@media print {
  .back-to-top {
    display: none;
  }
}