<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
  <style>
    .container {
      display: flex;
      justify-content: center;
      gap: 30px;
      margin: 10rem;
    }

    .child {
      width: 30px;
      height: 30px;
      border-radius: 50%;
    }

    .child:nth-child(1) {
      background-color: violet;
      animation: boxShadow1 1.5s ease-in-out infinite forwards;
    }

    .child:nth-child(2) {
      background-color: slateblue;
      animation: boxShadow2 1.5s ease-in-out infinite forwards;
      animation-delay: 0.3s;
    }

    .child:nth-child(3) {
      background-color: darkslateblue;
      animation: boxShadow3 1.5s ease-in-out infinite forwards;
      animation-delay: 0.6s;
    }

    @keyframes boxShadow1 {
      50% {
        box-shadow: 2px 2px 31px 0px violet;
      }

      100% {
        box-shadow: 0 0 0 0 violet;
      }
    }

    @keyframes boxShadow2 {
      50% {
        box-shadow: 2px 2px 31px 0px slateblue;
      }

      100% {
        box-shadow: 0 0 0 0 slateblue;
      }
    }

    @keyframes boxShadow3 {
      50% {
        box-shadow: 2px 2px 31px 0px darkslateblue;
      }

      100% {
        box-shadow: 0 0 0 0 darkslateblue;
      }
    }
  </style>
</head>

<body>
  <div class="container">
    <span class="child"></span>
    <span class="child"></span>
    <span class="child"></span>
  </div>
</body>

</html>

External CSS

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External JavaScript

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