Hello. I am making a web application and I want for when the user clicks a certain button for there to be a "pop up." Not really a pop up, but rather a little window in the browser is created and the rest of the screen is unable to be edited and is darker. Face book has such an effect, but I can't recall where. Also, this http://demo.atmail.org/ has that effect. How the login window is above the regular window and the regular window can not be touched.
What exactly is that effect called(so I can search for it!) and does C# have anything that can do that without hand coding the javascript?