title: CSS height set to percent, is it relative to the parents content box, or padding box, etc
body: <p><a href="https://developer.mozilla.org/en-US/docs/Web/CSS/height" rel="nofollow">MDN</a> says:</p>
  
  <pre><code>The percentage is calculated with respect to the height of the generated box's containing block.
  </code></pre>
  
  <p>So we have a containing block that contains a child element. The child element has <code>height: 100%</code> or some other percent.</p>
  
  <p>If the containing block has height, padding, and border set, is the child elements height calculated as 100% of the containing block's content-box height, padding-box height, border-box height?</p>
  
  <p>If we change the box-sizing of the container block, but also make other changes such that the container block's content-box/padding-box/border-box sizes do not change, is the size of the child element affected?</p>
  
  <p>EDIT: apparently padding-box is experimental and only supported by FF.</p>