<div class="box first"></div>
<div class="box second"></div>
.box {
  width: 100px;
  height: 100px;
  padding: 20px;
  border: 5px solid;
  display: inline-block;
}

.first.box {
  box-sizing: content-box;
  background-color: skyblue;
}

.second.box {
  box-sizing: border-box;
  background-color: peachpuff;
}

External CSS

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External JavaScript

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