纯css的loading效果(参考https://github.com/tobiasahlin/SpinKit)

demo.html

<div class="loading">
  <div class="sk-fading-circle">
    <div class="sk-circle1 sk-circle"></div>
    <div class="sk-circle2 sk-circle"></div>
    <div class="sk-circle3 sk-circle"></div>
    <div class="sk-circle4 sk-circle"></div>
    <div class="sk-circle5 sk-circle"></div>
    <div class="sk-circle6 sk-circle"></div>
    <div class="sk-circle7 sk-circle"></div>
    <div class="sk-circle8 sk-circle"></div>
    <div class="sk-circle9 sk-circle"></div>
    <div class="sk-circle10 sk-circle"></div>
    <div class="sk-circle11 sk-circle"></div>
    <div class="sk-circle12 sk-circle"></div>
  </div>
</div>

loading.css

    .sk-fading-circle {
      margin: 0 auto;
      width: 80px;
      height: 80px;
      position: relative;
    }

    .sk-fading-circle .sk-circle {
      width: 100%;
      height: 100%;
      position: absolute;
      left: 0;
      top: 0;
    }

    .sk-fading-circle .sk-circle:before {
      content: '';
      display: block;
      margin: 0 auto;
      width: 15%;
      height: 15%;
      background-color: #fff;
      border-radius: 100%;
      -webkit-animation: sk-circleFadeDelay 1.2s infinite ease-in-out both;
      animation: sk-circleFadeDelay 1.2s infinite ease-in-out both;
    }

    .sk-fading-circle .sk-circle2 {
      -webkit-transform: rotate(30deg);
      -ms-transform: rotate(30deg);
      transform: rotate(30deg);
    }

    .sk-fading-circle .sk-circle3 {
      -webkit-transform: rotate(60deg);
      -ms-transform: rotate(60deg);
      transform: rotate(60deg);
    }

    .sk-fading-circle .sk-circle4 {
      -webkit-transform: rotate(90deg);
      -ms-transform: rotate(90deg);
      transform: rotate(90deg);
    }

    .sk-fading-circle .sk-circle5 {
      -webkit-transform: rotate(120deg);
      -ms-transform: rotate(120deg);
      transform: rotate(120deg);
    }

    .sk-fading-circle .sk-circle6 {
      -webkit-transform: rotate(150deg);
      -ms-transform: rotate(150deg);
      transform: rotate(150deg);
    }

    .sk-fading-circle .sk-circle7 {
      -webkit-transform: rotate(180deg);
      -ms-transform: rotate(180deg);
      transform: rotate(180deg);
    }

    .sk-fading-circle .sk-circle8 {
      -webkit-transform: rotate(210deg);
      -ms-transform: rotate(210deg);
      transform: rotate(210deg);
    }

    .sk-fading-circle .sk-circle9 {
      -webkit-transform: rotate(240deg);
      -ms-transform: rotate(240deg);
      transform: rotate(240deg);
    }

    .sk-fading-circle .sk-circle10 {
      -webkit-transform: rotate(270deg);
      -ms-transform: rotate(270deg);
      transform: rotate(270deg);
    }

    .sk-fading-circle .sk-circle11 {
      -webkit-transform: rotate(300deg);
      -ms-transform: rotate(300deg);
      transform: rotate(300deg);
    }

    .sk-fading-circle .sk-circle12 {
      -webkit-transform: rotate(330deg);
      -ms-transform: rotate(330deg);
      transform: rotate(330deg);
    }

    .sk-fading-circle .sk-circle2:before {
      -webkit-animation-delay: -1.1s;
      animation-delay: -1.1s;
    }

    .sk-fading-circle .sk-circle3:before {
      -webkit-animation-delay: -1s;
      animation-delay: -1s;
    }

    .sk-fading-circle .sk-circle4:before {
      -webkit-animation-delay: -0.9s;
      animation-delay: -0.9s;
    }

    .sk-fading-circle .sk-circle5:before {
      -webkit-animation-delay: -0.8s;
      animation-delay: -0.8s;
    }

    .sk-fading-circle .sk-circle6:before {
      -webkit-animation-delay: -0.7s;
      animation-delay: -0.7s;
    }

    .sk-fading-circle .sk-circle7:before {
      -webkit-animation-delay: -0.6s;
      animation-delay: -0.6s;
    }

    .sk-fading-circle .sk-circle8:before {
      -webkit-animation-delay: -0.5s;
      animation-delay: -0.5s;
    }

    .sk-fading-circle .sk-circle9:before {
      -webkit-animation-delay: -0.4s;
      animation-delay: -0.4s;
    }

    .sk-fading-circle .sk-circle10:before {
      -webkit-animation-delay: -0.3s;
      animation-delay: -0.3s;
    }

    .sk-fading-circle .sk-circle11:before {
      -webkit-animation-delay: -0.2s;
      animation-delay: -0.2s;
    }

    .sk-fading-circle .sk-circle12:before {
      -webkit-animation-delay: -0.1s;
      animation-delay: -0.1s;
    }

    @-webkit-keyframes sk-circleFadeDelay {

      0%,
      39%,
      100% {
        opacity: 0;
      }

      40% {
        opacity: 1;
      }
    }

    @keyframes sk-circleFadeDelay {

      0%,
      39%,
      100% {
        opacity: 0;
      }

      40% {
        opacity: 1;
      }
    }

    .loading {
      background-color: #313131;
      width: 100px;
      height: 90px;
      padding: 20px;
      border-radius: 6px;
      opacity: 0.7;
      position: fixed;
      top: 50%;
      left: 50%;
      margin-left: -70px;
      margin-top: -45px;
      z-index: 99;
    }