<div class="container">
  <div class="box"></div>
  <div class="box"></div>
</div>
body{
  margin: 0;
  padding: 0;
  background: #344;
}


.container{
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%,-50%);
  width: 60px;
  height: 60px;
}

.box{
  position: absolute;
  width: 30px;
  height: 30px;
  background: #e74c3c;
}

.box:nth-child(1){
  animation: a1 2s infinite linear;
}

.box:nth-child(2){
  animation: a2 2s infinite linear;
}


@keyframes a1 {
  0%{
    top: 0;
    left: 0;
    width: 30px;
    height: 30px;
  }
  12.5%{
    top: 0;
    left: 0;
    width: 60px;
    height: 30px;
  }
  25%{
    top: 0;
    left: 0;
    width: 60px;
    height: 30px;
  }
  37.5%{
    top: 0;
    left: 30px;
    width: 30px;
    height: 30px;
  }
  50%{
    top: 0;
    left: 30px;
    width: 30px;
    height: 30px;
  }
  62.5%{
    top: 0;
    left: 30px;
    width: 30px;
    height: 60px;
  }
  75%{
    top: 0;
    left: 30px;
    width: 30px;
    height: 60px;
  }
  87.5%{
    top: 30px;
    left: 30px;
    width: 30px;
    height: 30px;
  }
  100%{
    top: 30px;
    left: 30px;
    width: 30px;
    height: 30px;
  }
}

@keyframes a2 {
  0%{
    right: 0;
    bottom: 0;
    width: 30px;
    height: 30px;
  }
  12.5%{
    right: 0;
    bottom: 0;
    width: 30px;
    height: 30px;
  }
  25%{
    right: 0;
    bottom: 0;
    width: 60px;
    height: 30px;
  }
  37.5%{
    right: 0;
    bottom: 0;
    width: 60px;
    height: 30px;
  }
  50%{
    right: 30px;
    bottom: 0;
    width: 30px;
    height: 30px;
  }
  62.5%{
    right: 30px;
    bottom: 0;
    width: 30px;
    height: 30px;
  }
  75%{
    right: 30px;
    bottom: 0;
    width: 30px;
    height: 60px;
  }
  87.5%{
    right: 30px;
    bottom: 0;
    width: 30px;
    height: 60px;
  }
  100%{
    right: 30px;
    bottom: 30px;
    width: 30px;
    height: 30px;
  }
}
/*
* https://www.darkcode.info/2019/09/loading-animation-using-only-html-css.html
*/
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