func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize
    {
        let heightOffset = (UIDevice.current.orientation.isPortrait) ? CGFloat(30) : CGFloat(0)

        let width = UIScreen.main.bounds.width
        let height = UIScreen.main.bounds.height - heightOffset

        return CGSize(width: width, height: height / CGFloat(mainScreenItems.count))
    }