SOURCE

<div class="loading"></div>
<div class="loading-pulse"></div>
<div class="loading loading--double"></div>

@-webkit-keyframes spin {
  0% {
    -webkit-transform: rotate(0deg);
            transform: rotate(0deg);
  }
  100% {
    -webkit-transform: rotate(360deg);
            transform: rotate(360deg);
  }
}
@keyframes spin {
  0% {
    -webkit-transform: rotate(0deg);
            transform: rotate(0deg);
  }
  100% {
    -webkit-transform: rotate(360deg);
            transform: rotate(360deg);
  }
}
@-webkit-keyframes pulse {
  50% {
    background: white;
  }
}
@keyframes pulse {
  50% {
    background: white;
  }
}
html, body {
  height: 100%;
}

body {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-justify-content: space-around;
      -ms-flex-pack: distribute;
          justify-content: space-around;
  -webkit-box-align: center;
  -webkit-align-items: center;
      -ms-flex-align: center;
          align-items: center;
  background: #333333;
}

.loading {
  border-radius: 50%;
  width: 24px;
  height: 24px;
  border: 0.25rem solid rgba(255, 255, 255, 0.2);
  border-top-color: white;
  -webkit-animation: spin 1s infinite linear;
          animation: spin 1s infinite linear;
}
.loading--double {
  border-style: double;
  border-width: .5rem;
}

.loading-pulse {
  position: relative;
  width: 6px;
  height: 24px;
  background: rgba(255, 255, 255, 0.2);
  -webkit-animation: pulse 750ms infinite;
          animation: pulse 750ms infinite;
  -webkit-animation-delay: 250ms;
          animation-delay: 250ms;
}
.loading-pulse:before, .loading-pulse:after {
  content: '';
  position: absolute;
  display: block;
  height: 16px;
  width: 6px;
  background: rgba(255, 255, 255, 0.2);
  top: 50%;
  -webkit-transform: translateY(-50%);
          transform: translateY(-50%);
  -webkit-animation: pulse 750ms infinite;
          animation: pulse 750ms infinite;
}
.loading-pulse:before {
  left: -12px;
}
.loading-pulse:after {
  left: 12px;
  -webkit-animation-delay: 500ms;
          animation-delay: 500ms;
}