iOS round bordered UIButton with a shadow written in Swift

RoundBorderedShadowButton.swift

import UIKit

class RoundBorderedShadowButton: UIButton {

    // Customize your button here
    let fillColor: UIColor = .white
    let highlightedFillColor: UIColor = .lightGray
    let borderColor: UIColor = .gray
    let borderWidth: CGFloat = 0.5
    let shadowColor: UIColor = .lightGray
    let shadowOffset: CGSize = CGSize(width: 0, height: 4)
    let shadowRadius: CGFloat = 15
    let shadowOpacity: Float = 1


    override init(frame: CGRect) {
        super.init(frame: frame)

        setup()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)

        setup()
    }

    override var isHighlighted: Bool {
        didSet {
            if isHighlighted {
                shadowLayer.fillColor = highlightedFillColor.cgColor
                shadowLayer.borderColor = highlightedFillColor.cgColor
            }
            else {
                shadowLayer.fillColor = fillColor.cgColor
                shadowLayer.borderColor = borderColor.cgColor
            }
        }
    }

    private func setup() {
        // Create a shape layer with borders
        shadowLayer = CAShapeLayer()
        shadowLayer.strokeColor = borderColor.cgColor
        shadowLayer.lineWidth = borderWidth
        shadowLayer.fillColor = fillColor.cgColor
        shadowLayer.path = UIBezierPath(ovalIn: layer.bounds).cgPath

        // Set the shadow of the shape layer
        shadowLayer.shadowPath = shadowLayer.path
        shadowLayer.shadowColor = shadowColor.cgColor
        shadowLayer.shadowOffset = shadowOffset
        shadowLayer.shadowRadius = shadowRadius
        shadowLayer.shadowOpacity = shadowOpacity

        // Add a shadowed shape layer to the bottom
        layer.insertSublayer(shadowLayer, at: 0)

        // Bring the image to the front
        // If you use title, then bring title (I haven't tested in yet)
        if let imageView = imageView {
            bringSubviewToFront(imageView)
        }
    }

    private var shadowLayer: CAShapeLayer!

}