title: postcss - css variable as argument inside postcss-mixins
body: <p>I have a mixin made with <a href="https://github.com/postcss/postcss-mixins" rel="nofollow noreferrer">postcss-mixins</a> and I want to use a css variable as argument, but it isn't working.</p>
  
  <pre><code>:root {
      --padd: 2rem;
  }
  
  @define-mixin position $place, $val {
      @if $place == end { right: $(val); }
      @if $place == start { left: $(val); }
  }
  </code></pre>
  
  <p>And then I call it:</p>
  
  <pre><code>.foo1 {
     @mixin position end, 2rem; /* it works -&gt; right: 2rem; */
  }
  
  .foo2 {
     @mixin position end, var(--padd); /* doesn't work -&gt; right: var(--padd); - it should output 2rem  */
  }
  </code></pre>
  
  <p>How can I manage to be able using css variables with postcss-mixins?</p>