Any trick to use opacity on a panel in Visual Studio Window Form?

Question

I recently started exploring Visual Studio. I was trying to create a slide menu. More specifically, when the user would press the button a submenu would pop up to the right.

Answer 1

Set any color at the panel. For example, black, after which you just need to register the TransparencyKey shape and select the color you want to make transparent:

 public Form1()
        {
            InitializeComponent();
            panel1.BackColor = Color.Black; 
            this.TransparencyKey = Color.Black;
        }