...it seems are geared up to wide screen but most are.
As I understand it in simple terms a web page is designed for a certain resolution. If that page is displayed at that designed resolution it will appear full screen. If the screen is of a lower resolution it will display but with scroll bars bottom and side. If the screen is of a greater resolution it will show space either side of the page displayed.
If the web designer is clever I believe the web site can be set up to interrogate the browser being used and send a page appropriate to the resolution being displayed.
My understanding anyway!