title: Mix two colors in sass
body: <p>Say I have these variables in a sass file:</p>
  <pre><code>$steel-blue: rgba(74, 148, 181,1)!default;
  $black: rgba(0, 0, 0,1)!default;
  
  $primary-color: $steel-blue;
  $background-color: $black;
  
  $primary-color-overlay: rgba($primary-color,8%);
  </code></pre>
  <p>I want to mix <code>$background-color</code> with <code>$primary-color-overlay</code> which should give me: <code>#060C0E</code>.</p>
  <p>I tried using <code>mix()</code> function but to no avail. It should be as if I have a placed <code>$primary-color-overlay</code> on top of <code>$background-color</code>.</p>
  <p>I'd like to saved the combined color as a variable too.</p>