For Dark Mode Medium Article

ViewController & Constants.swift

import UIKit
// ViewController.swift

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        //view.backgroundColor = .systemRed
        view.backgroundColor = CustomColor.customBackgroundColor
        
    }
}

// ----------------------------------------------------------------

// Constants.swift
enum CustomColor {
    
    static let customBackgroundColor  = UIColor(named: "BackgroundColor")
    static let customButtonColor      = UIColor(named: "ButtonBackgroundColor")
    static let customLabelColor       = UIColor(named: "LabelColor")
}