keyframes

@-webkit-keyframes passdown
{
  0%   {bottom:9%;}
  50%  {bottom:7.2%;}
  100% {bottom:9%;}
}
.pub-passdown{
  position: absolute;
  width: 10%;
  left: 45%;
  bottom: 4%;
  -webkit-animation-name: passdown;
  -webkit-animation-timing-function: ease;
  -webkit-animation-duration: 0.8s;
  -webkit-animation-iteration-count: infinite;
}