Layout of my intranet website was change when I access it on different computers

Good day!
I created my website on my computer and now I put it on my testing server and I found out that the size background of my website was change even I used those css code:

Code:

[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]<style type="text/css">[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]html,body{[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]overflow:hidden;[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]}[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]BODY {[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]background-image: url(bground.png);[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]background-attachment: fixed;[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]}[/SIZE][/FONT]
[FONT=Calibri][SIZE=3]</style>[/SIZE][/FONT]
[SIZE=3][FONT=Calibri] 

I used those codes to fixed the background but my problem is the background was doubled the image although it is fixed. Not only was the background change also the content of my website was dislocated. I want is only one output should be display in all computers.
It is possible that my website display should be dependent on the browser or the settings of the computer? So those in all computers the display of my website are all the same like what I browse in the internet?
On my used computers my website display is good, but when I try to other computers it was display not so good I don’t know why. I need to fix it now because all the staff wants to see my website… I hope you can help me…
Thank you

 

Have you fixed the length and breadth of the image or the monitor and/or browser you are using now is different.
You should give things in percent so that it can shorten or broaden the display according to screen resolution