SOURCE

<div class="box">
  <div>
    <span>
    </span>
  </div>
  <div>
    <span>
    </span>
  </div>
</div>

.box {
  margin: 50px auto;
  width: 100px;
  height: 100px;
  /* background-color: #fff; */
	position: relative;
	&:after{
		content: "";
		position: absolute;
		top: 0;
		left: 0;
		bottom: 0;
		right: 0;
		margin: auto;
		display: block;
		width: 0;
		height: 0;
		border: 40px solid #fff;
		border-radius: 50%;
		background-color: #fff;
	}
  > div {
    overflow: hidden;
    position: relative;
    width: 50px;
    height: 100px;
    > span {
      border: 50px solid rgba(0, 255, 255, .4);
      border-bottom-color: transparent;
      border-left-color: transparent;
      border-radius: 50%;
      display: block;
      height: 0;
      position: absolute;
      right: 0;
      top: 0;
      transform: rotate(225deg);
      width: 0;
			animation-duration: 4s;
      animation-iteration-count: infinite;
      animation-timing-function: linear;
    }
    &:nth-child(1) {
      /* background-color: red; */
      transform: rotate(180deg);
      float: left;
      span {
        animation-name: span1;
      }
    }
    &:nth-child(2) {
      float: right;
      /* background-color: grey; */
      span {
        animation-name: span2;
      }
    }
  }
}

@keyframes span1 {
  0% {
    transform: rotate(225deg);
  }
  50% {
    transform: rotate(225deg);
  }
  100% {
    transform: rotate(405deg);
  }
}

@keyframes span2 {
  0% {
    transform: rotate(225deg);
  }
  50% {
    transform: rotate(405deg);
  }
  100% {
    transform: rotate(405deg);
  }
}