title: Why would height specified as 1.0em be slightly less than font-size instead of equal?
body: <p>Consider the following display from the Chrome debugger showing the styles on an element:</p>
  
  <pre><code>font-size: 18px;
  height: 17.600000381469727px;
      .a, .h, .r - 1.0em
  left: 52.80000305175781px;
  line-height: 17.600000381469727px;
      .a, .h, .r - 1.0em
  </code></pre>
  
  <p>My understanding is that since height is specified as 1.0em, then its value in pixels should precisely equal to the font-size; instead it's 0.4 pixels smaller for some reason. There are no effects of padding or margin.</p>
  
  <p>The confusing thing is that in an earlier version things were working fine:</p>
  
  <pre><code>font-size: 18px;
  height: 18px;
      .stone, .iw-capture - 1em
  line-height: 18px;
      .stone, .mark, .iw-capture - 1.0em
  </code></pre>
  
  <p>So there's nothing fundamentally wrong with the browser's ability to do math. However, I can't figure out what changed to result in the odd behavior, or for that matter why anything changing should have an effect on this.</p>
  
  <p>Any thoughts on why this could be happening or what I'm missing?</p>