title: font size expressed with divisor?
body: <p>Today I came accross the following css snippet:</p>
  
  <pre><code>#navigation {
      font: bold 12px/18px "Trebuchet MS", Helvetica, Arial, sans-serif;
  }
  </code></pre>
  
  <p>I can't find information about this in the <a href="https://developer.mozilla.org/fr/docs/Web/CSS/font-size" rel="nofollow">font-size section</a> of the MDN.</p>
  
  <p>Could anyone give me a quick explanation of how it works?</p>