SOURCE

<div class="sk-double-bounce">
        <div class="sk-child sk-double-bounce1"></div>
        <div class="sk-child sk-double-bounce2"></div>
      </div>

body{
  background-color: #2c3e50;
}
.sk-double-bounce {
  width: 40px;
  height: 40px;
  position: relative;
  margin: 40px auto; }
  .sk-double-bounce .sk-child {
    width: 100%;
    height: 100%;
    border-radius: 50%;
    background-color: #FFF;
    opacity: 0.6;
    position: absolute;
    top: 0;
    left: 0;
    -webkit-animation: sk-doubleBounce 2s infinite ease-in-out;
            animation: sk-doubleBounce 2s infinite ease-in-out; }
  .sk-double-bounce .sk-double-bounce2 {
    -webkit-animation-delay: -1.0s;
            animation-delay: -1.0s; }

@-webkit-keyframes sk-doubleBounce {
  0%, 100% {
    -webkit-transform: scale(0);
            transform: scale(0); }
  50% {
    -webkit-transform: scale(1);
            transform: scale(1); } }

@keyframes sk-doubleBounce {
  0%, 100% {
    -webkit-transform: scale(0);
            transform: scale(0); }
  50% {
    -webkit-transform: scale(1);
            transform: scale(1); } }