.ds-top.ds-is-visible, .ds-top.ds-fade-out, .no-touch .ds-top:hover {
  -webkit-transition: opacity .3s 0s, visibility 0s 0s;
  -moz-transition: opacity .3s 0s, visibility 0s 0s;
  transition: opacity .3s 0s, visibility 0s 0s;
}
.ds-top.ds-is-visible {
  /* the button becomes visible */
  visibility: visible;
  opacity: 1;

}
.ds-top.ds-fade-out {
  /* if the user keeps scrolling down, the button is out of focus and becomes less visible */
  opacity: .5;
}