.back-to-top {
  display: none;
  position: fixed;
  bottom: 50%;
  right: 20px;
  z-index: 9999;
  font-size: 18px;
  color: #FCFCFCf;
  background-color: #;
  border: none;
  outline: none;
  cursor: pointer;
  padding: 0px;
  border-radius: 8px;
}
 
.back-to-top:hover {
  box-shadow: 0px 5px 10px 0px rgba(0, 0, 0, 0.5);
}
 
.visible {
  display: flex;
}