.back-to-top {
  position: fixed;
  z-index: 1000;
  width: 40px; 
  height: 40px;
  padding: 7px 10px; 

  bottom: 50px;
  right: 20px;
  opacity: 0;

  -webkit-border-radius: 3px;
  -moz-border-radius: 3px;
  border-radius: 3px;

  background-color: rgba(0, 0, 0, 0.2);
  transition: 0.2s ease;

}

.back-to-top:hover {
  background-color: rgba(0, 0, 0, 0.3);
}

.back-to-top path {
  fill: #fff;
}