Laravel Excel / PHPExcel，应用样式存储行数

Question

I've created an array out of an object that I'm dumping to excel with Laravel excel/PHPExcel, but I 've made an array that stores the count of rows for the top level of the $allGroupResult array so that I can individually style those rows.

The row numbers stored in $boldRows are the rows that I want bold and to have a different width on those cells.

How can I apply the row count from $boldRows so that I can apply unique styling to those rows only?

$allgroupResult= array();
    $rowCount = 2;
    $boldRows = array();

    foreach($prices->groups as $group){ 

        //creating array items omitted 

        array_push($allgroupResult, $groupItem);    
        array_push($boldRows, $rowCount++);

        foreach($group->skus as $sku){

            //creating array items omitted

            array_push($allgroupResult, $skuItem);
            $rowCount++;    
        }
    }

    $name = 'File Export';

    $build = Excel::create($name, function ($excel) use ($allgroupResult) {

        $excel->setTitle('File Export');

        $excel->sheet('File Export', function ($sheet) use ($allgroupResult) {

            $sheet->fromArray($allgroupResult);

            // Not sure how to use $boldRows count here to make bold, wider cells, etc.
            $sheet->getStyle('A1:'.$sheet->getHighestColumn().'1')->getFont()->setBold(true);
   }