HTML CODE

Hello,
WOW, what a site!!
1. Here only I found the answer which html code to use to close an html page (like clicking on the "X" on the top right corner).
But a window pops asking for OK to close the window, how do I eliminate this window - so the page will close when clicking on the button, without any further questions?
This I could not find, and I will appreciate much any help.
Thanks and best Regards!
Mordechai