title: what does \ mean in a css hex color notation?
body: <p>I'm curious what something like this means in CSS:</p>
  
  <pre class="lang-css prettyprint-override"><code>background-color: #080808 \9;
  </code></pre>
  
  <p>I know the hex color notation, of course, but I've never seen \9 used before. Even looking at the w3c, I'm not sure they define it either: <a href="http://dev.w3.org/csswg/css3-color/#colorunits">color units</a></p>