title: Is there something like "+=" in SASS?
body: <p>Is it possible to redefine a numerical attribute in SASS by increment or decrement? Consider something like this:</p>
  
  <pre><code>h1 {
      font-size: 10px;
  }
  
  h1.important {
      font-size: += 10px;
  }
  </code></pre>
  
  <p>I know that I can work around that by defining a variable. Is it possible to do this without?</p>