// For debugging purposes
@IBAction func showCards(_ sender: UIButton) {
    for index in cardButtons.indices {
        let button = cardButtons[index]
        let card = game.cards[index]
        if !card.isMatched {
            button.setTitle(emoji(for: card), for: UIControl.State.normal)
            button.backgroundColor = #colorLiteral(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
        }
    }

}
@IBAction func hideCards(_ sender: UIButton) {
    for index in cardButtons.indices {
        let button = cardButtons[index]
        let card = game.cards[index]
        if !card.isMatched, index != curIndex {
            button.setTitle("", for: UIControl.State.normal)
            button.backgroundColor = card.isMatched ? #colorLiteral(red: 0.9254940748, green: 0.1921561658, blue: 0.3890609741, alpha: 0) : #colorLiteral(red: 1, green: 0.5763723254, blue: 0, alpha: 1)
        }
    }
}