<html>
<body>
  <div class="parent">
    <div class="child"></div>
  </div>
    
</body>
</html>
* {
    margin: 0;
    padding: 0;
}

.parent {
  height: 100vh;
  width: 100%;
  background: #555c63;
  
  /* center div using flexbox */
  display: flex; 
  justify-content: center; /*To center div horizontally */
  align-items:center;  /* center div vertically */
}

.child {
  height: 60px;
  width: 60px;
  background: red;
}

External CSS

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External JavaScript

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