SOURCE

<div class="loading"></div>

.loading{
  width:200px;
  height:200px;
  border:1px solid red;
  position:relative;
}
.loading::before,.loading::after{
  content:"";
  position:absolute;
  top:0;
  left:0;
  bottom:0;
  right:0;
  width:0px;
  height:0px;
  background:#000;
  border-radius:50%;
  margin:auto;
  animation: s 1.5s linear infinite;
}
.loading::after{
  animation-delay:0.75s;
}
@keyframes s{
  0%{
    width:0px;
    height0px;
    opacity：1
  }
  100%{
    width:100px;
    height:100px;
    opacity:0;
}