title: CSS calc() subtract negative value
body: <p>Is it OK to subtract a minus number, like this?</p>
  
  <pre><code>width: calc(35% - -20px);
  </code></pre>
  
  <p>Because if I do as above, it behaves differently than if I do this:</p>
  
  <pre><code>width: calc(35% + 20px);
  </code></pre>
  
  <p>Here you can see the difference:
  <a href="http://nightly.gamempire.it/" rel="nofollow">http://nightly.gamempire.it/</a></p>
  
  <ul>
  <li>Put the window of the browser &lt; 1200px and > 1000px</li>
  <li>Analyze the #gallery_thumb element</li>
  </ul>
  
  <p>Actually you see that it has: calc(35% - -20px)
  If you change to calc(35% + 20px), it breaks (the #gallery_thumb will be less higher than the #gallery_img).</p>
  
  <p>Why is this? Can you not subtract a negative number?</p>