ButtonPanelView.swift

import UIKit

fileprivate let buttonSize: CGFloat = 56
fileprivate let shadowOpacity: Float = 0.7

class ButtonPanelView: UIView {

  lazy var menuButton: UIButton = {
    let button = UIButton(frame: .zero)
    button.setTitle("➕", for: .normal)
    button.backgroundColor = .clear
    button.layer.cornerRadius = buttonSize / 2
    button.addTarget(
      self, action: #selector(handleTogglePanelButtonTapped(_:)), for: .touchUpInside)
    return button
  }()

  lazy var dogButton: UIButton = {
    let button = UIButton(frame: .zero)
    button.setTitle("🐶", for: .normal)
    button.layer.cornerRadius = buttonSize / 2
    button.isHidden = true
    return button
  }()

  lazy var catButton: UIButton = {
    let button = UIButton(frame: .zero)
    button.setTitle("🐱", for: .normal)
    button.layer.cornerRadius = buttonSize / 2
    button.isHidden = true
    return button
  }()

  lazy var expandedStackView: UIStackView = {
    let stackView = UIStackView()
    stackView.axis = .vertical
    stackView.isHidden = true
    stackView.addArrangedSubview(dogButton)
    stackView.addArrangedSubview(catButton)
    return stackView
  }()

  lazy var containerStackView: UIStackView = {
    let stackView = UIStackView()
    stackView.axis = .vertical
    stackView.addArrangedSubview(expandedStackView)
    stackView.addArrangedSubview(menuButton)
    return stackView
  }()
  
  // ...
}