@keyframes pulse {
    0%    {opacity: 0; transform: scale(0);}
    50%   {opacity: 1; transform: none;}
    100%  {opacity: 0; transform: scale(0);}
}

.loading {
  animation-name: pulse;
  animation-duration: 1.25s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}