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body, html { height:100%; 
  margin:0; 
  padding:0;
  width:100%; 
  background-color:silver;
  text-align: center;
  }

#envoldura {
  border:1px solid black;
  width:99%;
  height:99%;    
  margin:auto;     
  text-align:center;
  font-size:300%;
}

#uno {
  border:1px solid black;
  width:49%;
  display:inline-block;     
  margin:auto;     
  height:49%;    
  background-color:red;
}

#dos {
  border:1px solid black;
  width:49%;
  display:inline-block;
  height:49%;    
  background-color:blue
}

#tres {
  border:1px solid black;
  width:49%;
  display:inline-block;
  height:49%;    
  background-color:green;
}

#cuatro {
  border:1px solid black;
  width:49%;
  display:inline-block;
  height:49%;    
  background-color:yellow;
}
  
#cinco{
  width: 200px;
  height: 200px;
  position: fixed;
  margin: -100px 0 0 -100px;
  background: cyan;
  top: 50%;
  left: 50%;
  border: 1px solid black;
}