title: Sass negative variable value?
body: <p>I have a couple of scss selectors where I use the same amount positive and negative, as in:</p>
  
  <pre><code>padding: 0 15px 15px;
  margin: 0 -15px 20px -15px;
  </code></pre>
  
  <p>I'd prefer to use a variable for all the 15px amounts, but this does not work:</p>
  
  <pre><code>$pad: 15px;
  padding: 0 $pad $pad;
  margin: 0 -$pad 20px -$pad;
  </code></pre>
  
  <p>The margin amounts convert to positive numbers.  Am I missing something?</p>