What is an example of violating LSP in .NET code?

Example (Violation of LSP):

public class Rectangle
{
public virtual int Width { get; set; }
public virtual int Height { get; set; }
public int Area() => Width * Height;
}
public class Square : Rectangle
{
public override int Width
{
set { base.Width = base.Height = value; }
}
public override int Height
{
set { base.Width = base.Height = value; }
}
}

Now if you substitute Rectangle with Square:

Rectangle rect = new Square();
rect.Width = 5;
rect.Height = 10;

Console.WriteLine(rect.Area()); // Outputs 100, but logically

expected 50

❌ The behavior is incorrect — this is a violation of LSP.