Leafo\ScssPhp\Compiler::collapseSelectors PHP Method

    protected function collapseSelectors($selectors)
    {
        $parts = [];
        foreach ($selectors as $selector) {
            $output = '';
            array_walk_recursive($selector, function ($value, $key) use(&$output) {
                $output .= $value;
            });
            $parts[] = $output;
        }
        return implode(', ', $parts);
    }