<div class="border-box">border-box/width:50%</div>
<div class="border-box">border-box/width:50%</div>
<div class="box">box/width:50%</div>
<div class="box">box/width:50%</div>


div:nth-of-type(2),
div:nth-of-type(4){
  border-color:red;
}
.border-box,
.box{
  width:50%; 
  height:100px;
  float:left; 
  background:#fff; 
  border: 5px solid #1b73ba;
}
.border-box{
  box-sizing: border-box;
   -moz-box-sizing: border-box;
   -webkit-box-sizing: border-box;
}

External CSS

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External JavaScript

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