ViewController.swift

import UIKit

class ViewController: UIViewController {
    
    private lazy var container: UIView = {
        let view = UIView()
        view.backgroundColor = .blue
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()
    
    private lazy var view1: UIView = {
        let view = UIView()
        view.backgroundColor = .red
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()
    
    private lazy var view2: UIView = {
        let view = UIView()
        view.backgroundColor = .green
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
        view.addSubview(container)
        container.addSubview(view1)
        container.addSubview(view2)
        
        NSLayoutConstraint.activate([
            container.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            container.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            container.widthAnchor.constraint(equalToConstant: 200),
            container.heightAnchor.constraint(equalToConstant: 200),
            
            view1.centerXAnchor.constraint(equalTo: container.centerXAnchor),
            view1.centerYAnchor.constraint(equalTo: container.centerYAnchor),
            view1.widthAnchor.constraint(equalToConstant: 100),
            view1.heightAnchor.constraint(equalToConstant: 100),
            
            view2.centerXAnchor.constraint(equalTo: container.centerXAnchor),
            view2.centerYAnchor.constraint(equalTo: container.centerYAnchor),
            view2.widthAnchor.constraint(equalToConstant: 50),
            view2.heightAnchor.constraint(equalToConstant: 50),
        ])
    }
}