.scroll-to-top {
  position: fixed;
  right: 20px;
  bottom: 20px;
  z-index: 1;
  background-color: #4CAF50;
  color: #fff;
  border: none;
  border-radius: 50%;
  padding: 10px;
  cursor: pointer;
  
}

/* target pseudo-class magic */
#top:target ~ .scroll-to-top {
  <!-- opacity: 1; /* visible when #top is targeted */ -->
  opacity: 0; /* initially hidden */
  transition: opacity 0.5s; /* fade-in effect */
}

#top:target ~ .scroll-to-top:hover {
  background-color: #3e8e41; /* hover effect */
}