<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="Width = device - width, initial - scale = 1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>The CSS in circles</title>
  <style>
    .turn{
      position: relative;
      width:100px;
      height: 100px;
      border: 10px solid #f4f4f4;
      animation:turn 1s linear infinite;      
      margin: 100px auto;
      border-radius: 50%; 
    }
    .turn::after{
      position: absolute;
      content: ' ';
      top:0px;
      left:10px;
      width: 12px;
      height: 12px;
      background: # 333;
      border-radius:50%; 
    }
     .turn::before{
      position: absolute;
      content: ' ';
      top: -4px;
      left:16px;
      width: 12px;
      height: 12px;
      background: blue;
      border-radius:50%; 
    }
    /* turn: the name of the defined animation 1s: the animation time linear: the animation trajectory to complete a cycle infinite: specifies that the animation should play an infinite number of times */
    @keyframes turn{
      0%{transform:rotate(0deg); 25%} {transform:rotate(90deg); 50%} {transform:rotate(180deg); 75%} {transform:rotate(270deg); 100%} {transform:rotate(360deg);}
    }
  </style>
</head>
<body>
  <div class="turn">
  </div>
</body>
</html>
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