title: Is the default font-size of every browser 16px? Why?
body: <p>CSS3 defines new a length unit for <code>font-size</code> called <code>rem</code>. This allow us to compute element's <code>font-size</code> relate to the root element (html element).</p>
  
  <p>To compute the <code>font-size</code> more easily , we usually assume the root element's <code>font-size</code> is <code>16px</code>, therefore the CSS usually ends up like this:</p>
  
  <pre><code>html { font-size:62.5%; } // 10px = 16px * 0.625
  </code></pre>
  
  <p>So, every element height with <code>rem</code> is relative to <code>10px</code>, for example </p>
  
  <pre><code>p{ font-size : 1.4rem ;} // 14px = 10px * 1.4 
  </code></pre>
  
  <p>I cant find why we assume we can multiply by <code>16px</code>? How can we trust every browser will have the same base value of <code>16px</code>? Is there is a standard description about the pre-defined <code>16px</code>?</p>
  
  <p><strong>Ref</strong></p>
  
  <ul>
  <li><a href="https://developer.mozilla.org/en-US/docs/Web/CSS/font-size" rel="noreferrer">MDN font-size</a></li>
  <li><a href="http://dev.w3.org/csswg/css-values-3/#font-relative-lengths" rel="noreferrer">W3C rem</a></li>
  <li><a href="http://caniuse.com/#feat=rem" rel="noreferrer">CanIUse about rem</a></li>
  <li><a href="https://github.com/dhg/Skeleton/blob/master/css/skeleton.css" rel="noreferrer">Github skeleton.css</a></li>
  </ul>