Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.2)
// Compass (v1.0.0.alpha.17)
// ----

@mixin background-opacity($theme) {

background-color: nth($theme, 1); //fallback
background-color: nth($theme, 2);

}
$dark: #000;
$dark-opacity: #ccc;

$dark-theme: $dark, $dark-opacity;

.class {
  @include background-opacity($dark-theme);
}

SassMeister-output.css

.class {
  background-color: black;
  background-color: #cccccc;
}