title: Using fraction (fr) in calc() gives "Invalid property value"
body: <p>I'm trying to use <code>calc()</code> on some widths while using CSS Grid. So one thing I'm trying is this:</p>
  
  <pre><code>grid-template-columns: calc(1fr - 50px) calc(1fr - 50px);
  </code></pre>
  
  <p>As I want it to be two fractions, but remove 50px since that is used for padding and such. However, when doing this, Chrome says: "Invalid property value".</p>
  
  <p>Can't <code>calc()</code> be used on fractions, or am I doing something wrong here?</p>