<div class="contentBox">
  <span class="contentBox__item">item</span>
</div>
.contentBox{
  position:relative;
  height:200px;
  background:#ddd;
}
.contentBox__item{
  position:absolute;
  top:50%;
  left:50%;
  margin-top:-25px;
  margin-left:-50px;
  width:80px;
  height:50px;
  background:blue;
  color:#fff;
}

External CSS

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External JavaScript

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