var collectionView: UICollectionView!
var titleLabel: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    self.view.translatesAutoresizingMaskIntoConstraints = false
    let margins = self.view.layoutMarginsGuide

    let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
    layout.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10)

    collectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
    layout.itemSize = CGSize(width: self.collectionView.frame.width / 4, height: self.collectionView.frame.width / 4)
    layout.minimumInteritemSpacing = self.collectionView.frame.width / 15
    layout.minimumLineSpacing = self.collectionView.frame.width / 5

    collectionView.backgroundColor = UIColor.black
    collectionView.dataSource = self
    collectionView.delegate = self
    collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")

    titleLabel = UILabel()
    titleLabel.translatesAutoresizingMaskIntoConstraints = false

    titleLabel.textAlignment = .center
    titleLabel.numberOfLines = 1
    titleLabel.font = UIFont.systemFont(ofSize: 22)
    titleLabel.backgroundColor = UIColor.lightGray
    titleLabel.text = "Challenges"
    titleLabel.textColor = UIColor.red

    let stackView = UIStackView(arrangedSubviews: [titleLabel, collectionView])
    stackView.backgroundColor = UIColor.white
    stackView.axis = .vertical
    stackView.distribution = .fillEqually
    stackView.alignment = .fill
    stackView.spacing = 5
    self.view.addSubview(stackView)
    stackView.translatesAutoresizingMaskIntoConstraints = false

    //stackView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
    //stackView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor).isActive = true
    stackView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
    stackView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
    stackView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
    stackView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
    stackView.heightAnchor.constraint(equalTo: self.view.heightAnchor, multiplier: 1.0).isActive = true

}