A container view helps drop shadow

ShadowContainer.swift

class ShadowContainer: UIView {
  init(child: UIView,
       shadowRadius: CGFloat = 2,
       shadowOffset: CGSize = CGSize.zero,
       shadowOpacity: Float = 0.3) {
    super.init(frame: CGRect.zero)
    translatesAutoresizingMaskIntoConstraints = false

    addSubview(child)
    child.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true
    child.trailingAnchor.constraint(equalTo: trailingAnchor).isActive = true
    child.topAnchor.constraint(equalTo: topAnchor).isActive = true
    child.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true

    layer.shadowRadius = shadowRadius
    layer.shadowOffset = shadowOffset
    layer.shadowOpacity = shadowOpacity
    layer.cornerRadius = child.layer.cornerRadius
  }

  required init?(coder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
}