如何将UIAppearance代理属性应用于UILabel？

import UIKit

class CustomUILabel: UILabel {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupAppearance()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setupAppearance()
    }
    
    private func setupAppearance() {
        // 在这里设置UIAppearance代理属性
    }
}

private func setupAppearance() {
    textColor = UIColor.red
    font = UIFont.systemFont(ofSize: 18)
    backgroundColor = UIColor.lightGray
}

UILabel.appearance() = CustomUILabel.self