30-seconds-of-code/snippets/box-sizing-reset.md

Box-sizing reset

Resets the box-model so that widths and heights are not affected by their borders or padding.

HTML

<div class="box">border-box</div>
<div class="box content-box">content-box</div>

CSS

html {
  box-sizing: border-box;
}
*,
*::before,
*::after {
  box-sizing: inherit;
}
.box {
  display: inline-block;
  width: 150px;
  height: 150px;
  padding: 10px;
  background: tomato;
  color: white;
  border: 10px solid red;
}
.content-box {
  box-sizing: content-box;
}

Demo

Explanation

1. box-sizing: border-box makes the addition of padding or borders not affect an element's width or height.
2. box-sizing: inherit makes an element respect its parent's box-sizing rule.

Browser support

✅ No caveats.

• https://caniuse.com/#feat=css3-boxsizing