title: Property -webkit-border-radius is an unknown vendor extension
body: <p>When I validate css3 I got this error.</p>
  
  <pre><code>Property -webkit-border-radius is an unknown vendor extension
  Property -moz-border-radius is an unknown vendor extension
  Property -webkit-border-radius is an unknown vendor extension
  </code></pre>
  
  <p>How can I get 100% CSS3 valid?</p>
  
  <pre><code>-webkit-border-radius: 50%;
  -moz-border-radius: 50%;
  border-radius:50%;
  </code></pre>