Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="bg">Hello</div>

SassMeister-input.scss

// ----
// Sass (v3.4.9)
// Compass (v1.0.1)
// ----

$success: #009900;
$secondary: #ffffff;

div {
  background-color: dark-light-diff($success, $secondary, 50%, -35%);
  width:300px;
  height: 50px;
  font-weight: bold;
  color: #919191;
}

@function bleh($input) {
  @return $input;
}

@function dark-light-diff($adjusted-color, $comparison-color, $lightness, $darkness) {
  @if brightness($adjusted-color) < brightness($comparison-color) {
    @return scale-color($adjusted-color, $lightness: $lightness)
  } @else {
    @return scale-color($adjusted-color, $lightness: $darkness)
  }
}

SassMeister-output.css

div {
  background-color: dark-light-diff(#009900, #ffffff, 50%, -35%);
  width: 300px;
  height: 50px;
  font-weight: bold;
  color: #919191;
}

SassMeister-rendered.html

<div class="bg">Hello</div>