Decorator.cs

abstract class Thing
    {
        private int price;
        private string detail;

        public int Price { get => price; set => price = value; }
        public string Detail { get => detail; set => detail = value; }

        public Thing(int price, string detail)
        {
            this.price = price;
            this.detail = detail;
        }

        public virtual void Plus(Thing something)
        {
            price += something.price;
            detail += ", " + something.detail;
        }
    }

    class Party : Thing
    {
        public Party(int price = 200, string detail = "Party") : base(price, detail)
        {
        }
       
    }

    class Alcohol : Thing
    {
        public Alcohol(int price = 50, string detail = "Alcohol") : base(price, detail)
        {
        }
        
    }

    class Girl : Thing
    {
        public Girl(int price = 1000, string detail = "Girl") : base(price, detail)
        {
        }
    }

    class Program
    {
        static void Main(string[] args)
        {

            Party A = new Party();
            Alcohol B = new Alcohol();
            Girl C = new Girl();

            Console.WriteLine($"{A.Detail}");
            Console.WriteLine($"{A.Price}");

            A.Plus(B);
            Console.WriteLine($"{A.Detail}");
            Console.WriteLine($"{A.Price}");

            A.Plus(C);
            Console.WriteLine($"{A.Detail}");
            Console.WriteLine($"{A.Price}");

            Console.ReadLine();
        }
    }