/* style it as you'd like */
.scroll-up {
  position: fixed;
  right: 25px;
  bottom: 25px;
  width: 50px;
  height: 50px;
  background-color: red;
  z-index: 9999;
  opacity: 0; /* it should be hidden initially */
  visibility: hidden;
  cursor: pointer;
  transition: all 0.3 ease;
}

/* helper class for toggling visibility */
.visible {
  opacity: 1 !important;
  visibility: visible !important;
}