Observations2.swift

struct Colors {
   static let backgroundButtonBackgroundColor = UIColor.clear
   static let backgroundButtonTintColor = #colorLiteral(red: 0.6000000238, green: 0.6000000238, blue: 0.6000000238, alpha: 1)
   static let foregroundButtonBackgroundColor = #colorLiteral(red: 1, green: 0.8, blue: 0, alpha: 1)
   static let foregroundButtonTintColor = #colorLiteral(red: 1, green: 1, blue: 1, alpha: 1)
 }

let shapeLayer = CAShapeLayer()
let backgroundButton = UIButton()
let foregroundButton = UIButton()

func setup() {
    UI: do {
        backgroundButton.setImage(UIImage(named: "search"), for: .normal)
        backgroundButton.backgroundColor = Colors.backgroundButtonBackgroundColor
        backgroundButton.tintColor = Colors.backgroundButtonTintColor

        foregroundButton.setImage(UIImage(named: "search"), for: .normal)
        foregroundButton.backgroundColor = Colors.foregroundButtonBackgroundColor
        foregroundButton.tintColor = Colors.foregroundButtonTintColor
    }
    layers: do {
        // the shape layer ( mask ) will hide/show the foreground button depending on the scroll animation progress
        foregroundButton.layer.mask = shapeLayer
        foregroundButton.layer.masksToBounds = true
    }
    layout: do {
        addSubview(backgroundButton)
        addSubview(foregroundButton)

        // layout buttons using autolayout there
    }
}