<div class="container"><div class="item"></div><div>
body
{
  background-color: #fcfcfc;  
}
.container
{
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
}
.item
{
  background-color: #ccc;
  border-radius: 3px;
  width: 200px;
  height: 100px; 
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.