Decorator Pattern: WIll not run

I am trying to implement the Decorator pattern, but I keep getting an error when I try to run my program. I cannot figure out why. I know it has something to with something not being an interface, but I have tried a bunch of changes and nothing is working. I appreciate any assistance!

      using System;
      using System.Collections.Generic;
      using System.Linq;
      using System.Text;
      using System.Threading.Tasks;

      namespace OODAssignment3_ZackDavidson
      {
      class Program
      {
       static void Main(string[] args)
       {
        //Creates a new Calvin Klein Shirt fordecoration
        CalvinKlein ckShirt = new CalvinKlein();
        Console.WriteLine(Convert.ToString(ckShirt.GetBrand()));

        //Puts a solid color on the Calvin Klein Shirt
        solidColorDecorator ckSCD = new solidColorDecorator(ckShirt);

        //Puts stripes on the Calvin Klein Shirt
        stripedShirtDecorator ckSSD = new stripedShirtDecorator(ckShirt);

        //Puts a pocket on the Clavin Klein Shirt
        pocketShirtDecorator ckPSD = new pocketShirtDecorator(ckShirt);

        //Creates a new Tommy Hilfiger Shirt
        TommyHilfiger thShirt = new TommyHilfiger();

        //Puts stripes on the Tommy Hilfiger Shirt
        stripedShirtDecorator thSSD = new stripedShirtDecorator(thShirt);

        //Puts a pocket on the Tommy Hilfiger Shirt
        pocketShirtDecorator thPSD = new pocketShirtDecorator(thShirt); 
    }//EndOfMain
}//EndOfClassProgram

public abstract class ShirtsComponent
{
    public abstract string GetBrand();
    public abstract double GetPrice();
}

class CalvinKlein : ShirtsComponent
{
    private string ck_Brand = "Calvin Klein";
    private double ck_Price = 75.0;

    public override string GetBrand()
    {
        return ck_Brand;
    }

    public override double GetPrice()
    {
        return ck_Price;
    }
}

class TommyHilfiger : ShirtsComponent
{
    private string th_Brand = "Tommy Hilfiger";
    private double th_price = 85.0;

    public override string GetBrand()
    {
        return th_Brand;
    }

    public override double GetPrice()
    {
        return th_price;
    }
}

public abstract class Decorator : ShirtsComponent
{
    ShirtsComponent fashion_Base = null;

    protected string _brand = "Undefined Decorator";
    protected double _price = 0.0;

    protected Decorator(ShirtsComponent fashionBase)
    {
        fashion_Base = fashionBase;
    }

    #region ShirtsComponent Members

    string ShirtsComponent.GetBrand()
    {
        return string.Format("{0}, {1}", fashion_Base.GetBrand(), _brand);
    }

    double ShirtsComponent.GetPrice()
    {
        return _price + fashion_Base.GetPrice();
    }
    #endregion
}

class solidColorDecorator : Decorator
{
    public solidColorDecorator(ShirtsComponent fashionBase)
        : base(fashionBase)
    {
        this._brand = "Solid Color Shirt";
        this._price = 25.0;
    }
}

class stripedShirtDecorator : Decorator
{
    public stripedShirtDecorator(ShirtsComponent fashionBase)
        : base(fashionBase)
    {
        this._brand = "Striped Shirt";
        this._price = 50.0;
    }
}

class pocketShirtDecorator : Decorator
{
    public pocketShirtDecorator(ShirtsComponent fashionBase)
        : base(fashionBase)
    {
        this._brand = "Dotted Shirt";
        this._price = 90.0;
    }
}

}//EndOfNamespace