title: W3C CSS validation error using calc() and vendor extensions
body: <p>After finishing my new HTML5/CSS3 template I proceeded to W3C validation.</p>
  
  <p>The result for HTML: "This document was successfully checked as HTML5!"</p>
  
  <p>The result for CSS: "Sorry! We found the following errors (1)"</p>
  
  <p>And the problem is around <code>height: calc(100vh - 80px);</code></p>
  
  <p>It also told me:</p>
  
  <pre class="lang-none prettyprint-override"><code>36      Property -ms-transform is an unknown vendor extension
  37      Property -webkit-transform is an unknown vendor extension
  112     Property -webkit-transition is an unknown vendor extension
  113     Property -moz-transition is an unknown vendor extension
  249     Property -webkit-background-size is an unknown vendor extension
  292     Property -webkit-background-size is an unknown vendor extension
  </code></pre>
  
  <p>So in this case what shall I do to get it 100% CSS3 valid?</p>