implement stack, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
                   
            stack st = new stack();
          while (true)
            {
                Console.Clear();
                Console.WriteLine("\nStack MENU(size -- 10)");
                Console.WriteLine("1. Add an element");
                Console.WriteLine("2. See the Top element.");
                Console.WriteLine("3. Remove top element.");
                Console.WriteLine("4. Display stack elements.");
                Console.WriteLine("5. Exit");
                Console.Write("Select your choice: ");
                int choice = Convert.ToInt32(Console.ReadLine());
                switch (choice)
                {
                    case 1:
                        Console.WriteLine("Enter an Element : ");
                        st.Push(Console.ReadLine());
                        break;
 
                    case 2: Console.WriteLine("Top element is: {0}", st.Peek());
                        break;
 
                    case 3: Console.WriteLine("Element removed: {0}", st.Pop());
                        break;
 
                    case 4: st.Display();
                        break;
 
                    case 5: System.Environment.Exit(1);
                        break;
                }
                Console.ReadKey();
            }
        }
    }
 
    interface StackADT
    {
        Boolean isEmpty();
        void Push(Object element);
        Object Pop();
        Object Peek();
        void Display();
    }
    class stack : StackADT
    {
        private int StackSize;
        public int StackSizeSet
        {
            get { return StackSize; }
            set { StackSize = value; }
        }
        public int top;
        Object[] item;
        public stack()
        {
            StackSizeSet = 10;
            item = new Object[StackSizeSet];
            top = -1;
        }
        public stack(int capacity)
        {
            StackSizeSet = capacity;
            item = new Object[StackSizeSet];
            top = -1;
        }
        public bool isEmpty()
        {
            if (top == -1) return true;
 
            return false;
        }
        public void Push(object element)
        {
            if (top == (StackSize - 1))
            {
                Console.WriteLine("Stack is full!");
            }
 
            else
            {
 
                item[++top] = element;
                Console.WriteLine("Item pushed successfully!");
            }
        }
        public object Pop()
        {
            if (isEmpty())
            {
                Console.WriteLine("Stack is empty!");
                return "No elements";
            }
            else
            {
 
                return item[top--];
            }
        }
        public object Peek()
        {
            if (isEmpty())
            {
 
                Console.WriteLine("Stack is empty!");
                return "No elements";
            }
            else
            {
                return item[top];
            }
        }
 
 
        public void Display()
        {
            for (int i = top; i > -1; i--)
            {
 
                Console.WriteLine("Item {0}: {1}", (i + 1), item[i]);
            }
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,12 sec, absolute running time: 0,11 sec, cpu time: 0,12 sec, average memory usage: 14 Mb, average nr of threads: 3, absolute service time: 0,28 sec