title: flex and flex-flow not validating
body: <p>For my school project, we're required to validate the CSS but for some reason, it refuses to accept flex as a display property and and display-direction as an attribute. I'm not sure if I made a mistake or if this is indeed correct. </p>
  
  <p>I even set the validator is validate CSS3. </p>
  
  <p><a href="http://www.css-validator.org/validator" rel="nofollow">http://www.css-validator.org/validator</a></p>
  
  <p><a href="http://www.w3schools.com/cssref/css3_pr_flex-flow.asp" rel="nofollow">http://www.w3schools.com/cssref/css3_pr_flex-flow.asp</a></p>
  
  <pre><code>.summary, .bio, .http, .terms, .citation {
  width:75%; 
  min-width: 812px; 
  margin:auto; 
  margin-top: 1em; 
  margin-bottom: 3em;
  display: flex;
  color: #585858;}
  
  .summary {
  flex-direction: row;}
  
  .bio, .terms, .citation {
  flex-direction: column;}
  
  figure{
  display: flex;}
  </code></pre>