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              <h2>No width specified on child so expands to fill parent width but applied padding and border are moved inwards, happy days.</h2>
<div class="parent">
  <div class="child">
    <p>content</p>
  </div>
</div>

<h2>But now for whatever reason I need to specify a width on my child element. Buggery my child has broken out.</h2>

<div class="parent">
  <div class="child withWidth">
    <p>content</p>
  </div>
</div>

<h2>I could adjust my child width but I need it be a %, this won't work mixed with pixel padding and borders - CSS box-sizing to the rescue!</h2>

<div class="parent">
  <div class="child withWidth boxPower">
    <p>content</p>
  </div>
</div>

<h2>And we're back to the original (desired) outcome but with an explicit % width mixed with pixel based padding and borders. Happy Days!</h2>

<h3>Now read these for the background...</h3>

<ul>
  <li><a href="http://paulirish.com/2012/box-sizing-border-box-ftw/">http://paulirish.com/2012/box-sizing-border-box-ftw/</a></li>
  <li><a href="https://css-tricks.com/box-sizing/">https://css-tricks.com/box-sizing/</a></li>
  <li><a href="http://html5please.com/#box-sizing">http://html5please.com/#box-sizing</a></li>
</ul>


            
          
!
            
              .parent{background: #ccc; width: 800px; padding: 20px 0;}
.child{background: #eee; padding: 50px; border: solid 1px #111;}

/* But now for whatever reason I need to specify a width on my child element... */
.withWidth{width: 100%;}

/* CSS box-sizing to the rescue! */
.boxPower{-webkit-box-sizing: border-box; -moz-box-sizing: border-box; box-sizing: border-box;}
            
          
!
999px
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