CodePen

HTML

            
              <div>
  Percentage sized and still centered.
</div>
            
          
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CSS

            
              body {
  background: #900;
}

div {
  position: absolute;
  left: 30%;
  right:30%;
  top: 25%;
  bottom:25%;
  
  padding: 20px;  
  background: red;
  color: white;
  text-align: center;
  box-shadow: 0 0 30px rgba(0, 0, 0, 0.2);
}
            
          
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JS

            
              
            
          
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