The "main content" you think doesn't have a border is just the body.
Your divs have no text in them yet. Add a few words in each div and you will see the white border extend down with them around #page div, but leaving the remainder of the body without a border.
If you want the body (ie the whole page) to have a border, move border: 1px solid #ffffff from #page to body in the head section.
Look at lots of online tutorials for div coding.
See http://www.wickham43.supanet.com/tutorial/links.html
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.