<div class="container">
   <div class="box"></div>
</div>
.container{
  height: 200px;
  background: lightblue;
  display: flex;
  flex-wrap: wrap;
  place-content: center center;
  width: 300px;
}
.box{
  width: 100px;
  height: 50px;
  background: red;
}

External CSS

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External JavaScript

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