protected function buildBootstrapCss(array $config)
    {
        $dir = $config['output_dir'];
        $inputs = $config['bootstrap_css']['inputs'];

        $inputs[] = 'assets/bootstrap-dialog/dist/css/bootstrap-dialog.min.css';

        return [
            'inputs'  => $inputs,
            'filters' => ['cssrewrite', 'less', 'yui_css'],
            'output'  => $dir . 'css/bootstrap.css',
            'debug'   => false,
        ];
    }