CodePen

HTML

            
              <div class="what"></div>
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              @keyframes "inOut" {
  0% {
    box-shadow: none;
  }
  25% {
    box-shadow: 0 0 0 10px white,
                0 0 0 20px black;
  }
  50% {
    box-shadow: 0 0 0 10px white,
                0 0 0 20px black,
                0 0 0 30px white,
                0 0 0 40px black;
  }
  75% {
    box-shadow: 0 0 0 10px white,
                0 0 0 20px black,
                0 0 0 30px white,
                0 0 0 40px black,
                0 0 0 50px white,
                0 0 0 60px black;
  }
  100% {
    box-shadow: 0 0 0 10px white,
                0 0 0 20px black,
                0 0 0 30px white,
                0 0 0 40px black,
                0 0 0 50px white,
                0 0 0 60px black,
                0 0 0 70px white,
                0 0 0 80px black;
  }
}

.what {
  margin: 20% auto;
  
  width: 100px;
  height: 100px;
  background: black;
  border-radius: 100%;
  
  animation-name: inOut;
  animation-duration: 1000ms;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
  animation-direction: alternate;
}
            
          
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JS

            
              
            
          
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