<div class="content-box">content-box</div>
<br>
<div class="border-box">border-box</div>
div {
  background-color: #ffb400;
  width: 200px;
  height: 200px;
  padding: 20px;
  margin: 40px;
  border: 4px solid black;
  
  font-size: 2rem;
  text-align: center;
}

.content-box {
  box-sizing: content-box; /* no need to specify ( defualt one)*/
}

.border-box {
  box-sizing: border-box; 
}

External CSS

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External JavaScript

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