CustomView for medium post about UICollectionView inside UIView

CustomView.swift

import UIKit

@IBDesignable
class CustomView: UIView {

    @IBOutlet var contentView: UIView!
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }
    
    private func commonInit() {
        let bundle = Bundle(for: type(of: self))
        bundle.loadNibNamed("CustomView", owner: self, options: nil)
        addSubview(contentView)
        contentView.frame = bounds
        contentView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        contentView.backgroundColor = .red
    }
}