         
         // CollectionView
         view.addSubview(collcetionView)
-        collcetionView.backgroundColor = .blue
         collcetionView.snp.makeConstraints { (make) in
             make.left.bottom.centerX.equalToSuperview()
             make.top.equalTo(tabBar.snp.bottom)

extension BQMainViewController: UICollectionViewDelegateFlowLayout {
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return collectionView.size
    }
}

private let mainCellReuseID = UICollectionViewCell.nameOfClass

class BQMainViewController: UIViewController {
    
    var itemSize = CGSize.zero
    
    // MARK: - Properties
    fileprivate lazy var subControllers: [UIViewController] = {
