.scrollup{
  position: fixed;
  right: 20px;
  bottom: 20px;
  cursor: pointer;
  transition: .3s;
  display: block;
  width: 40px; height: 40px;
  opacity: 0;
  visibility: hidden;
  background: url(./scrollup.png) 0 0 no-repeat;
  background-size: contain;
  z-index: 9000;
  overflow: hidden;
  text-indent: -9999px;
}
.scrollup:hover{
  background: url(./scrollup-hover.png) 0 0 no-repeat;
  background-size: contain;
}

.scrollup.active{
  opacity: 1;
  visibility: visible;
}