title: Why is the default font weight 400?
body: <p>So, when working with fonts :</p>
  
  <ul>
  <li>the default (aka "Regular") font weight is <strong>400</strong></li>
  <li>the "bold" font weight is <strong>700</strong></li>
  <li>the "light" font weight is <strong>300</strong></li>
  </ul>
  
  <p>But... why ? <strong>400</strong> what ? Is this a sort of unit ? Is there a historical reason behind that ?</p>