a#cRetour{
  border-radius:100px;
  padding:25px;
  font-size:20px;
  text-align:center;
  color:#fff;
  background:rgba(72, 40, 10, 0.5);
  position:fixed;
  right:30px;
  opacity:1;
  z-index:99999;
  transition:all ease-in 0.2s;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  text-decoration: none;
}
a#cRetour:before{ content: "\25b2"; }
a#cRetour:hover{
  background:rgba(0, 0, 0, 1);
  transition:all ease-in 0.2s;
}
a#cRetour.cInvisible{
  bottom:-35px;
  opacity:0;
  transition:all ease-in 0.2s;
}

a#cRetour.cVisible{
  bottom:20px;
  opacity:1;
}