Leafo\ScssPhp\Compiler::libInvert PHP Method

    protected function libInvert($args)
    {
        $value = $args[0];
        if ($value[0] === Type::T_NUMBER) {
            return null;
        }
        $color = $this->assertColor($value);
        $color[1] = 255 - $color[1];
        $color[2] = 255 - $color[2];
        $color[3] = 255 - $color[3];
        return $color;
    }