example.cs

sealed class Users
{
    public string name = "Stefan Djokic";
    public void GetName()
    {
        Console.WriteLine("Name: {0}", name);
    }
}
//Derived Class
public class Details : users //Error
{
    public int age = 27;
    public void GetAge()
    {
        Console.WriteLine("Age: {0}", age);
    }
}