#backtotop {
  background: #16a3e1 url(../images/up-arrow.png) no-repeat center center;
  bottom: 25px;
  cursor: pointer;
  display: none;
  height: 80px;
  position: fixed;
  right: 15px;
  text-indent:-9999px;
  width: 80px;
  z-index: 1;
  opacity: 0.8;
}

#backtotop:hover {
  opacity: 1;
}