#ur div here fam{
animation: float 6s ease-in-out infinite;}

@keyframes float {
  0% {
    box-shadow: 0 5px 15px 0px rgba(0,0,0,0.6);
    transform: translatey(0px);
  }
  50% {
    box-shadow: 0 25px 15px 0px rgba(0,0,0,0.2);
    transform: translatey(-20px);
  }
  100% {
    box-shadow: 0 5px 15px 0px rgba(0,0,0,0.6);
    transform: translatey(0px);
  }
}