<!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>
</head>
<body>
  <div class="a1"></div>
  <div class="a2"></div>
  <div class="a3"></div>
</body>
</html>
.a1, .a2, .a3 {
  width: 50px;
  height: 50px;
  
}

.a1 {
  background-color: red;
/*   position: absolute; */
}
.a2 {
  
  background-color: green;
  position: absolute;
  top: auto;
}
.a3 {
  background-color: blue;
}

External CSS

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External JavaScript

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