.back-to-top {
  position: fixed;
  right: 50px;
  bottom: 50px;
  z-index: 7;
  display: flex;
  flex-direction: row;
  justify-content: center;
  align-items: center;
  width: 41px;
  height: 41px;
  border-radius: 50%;
  background-color: #007da5;
  box-shadow: 0 9px 12px 0 rgba(0, 0, 0, 0.09);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transition: opacity .2s linear, visibility .2s linear, bottom .2s linear;
}

.back-to-top.-active {
  opacity: 1;
  visibility: visible;
}

.back-to-top.-fixed {
  position: absolute;
}