Need help with one Resolution.

hello everyone, since long time need set the exactly resolution for my web site i saw many tutorials and guides etc etc, but cant found the Exaclty Code …
The things is, When i Hold Control + – or + change the image and Going more small or bigged i need one still image!! centered that does not move and this always statically by more than use the mouse scroll, that this does not move and stay always fixed. my current values are

`body.light_theme {
background-attachment: scroll;
background-color: #fff!important;
background-image: url(“images/background-2.png”)!important;
no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}

—
and my website is this
http://www.vskgaming.com.ar/shop

And on my Forum i Set the Right Resolution, but Cant emulate the same on my other web page.. this are my Forum place
http://vskgaming.com.ar/foro/ <—- i need the same Fixed image same same
if press and hold Control + – or + here The image dont move and i want to make that same on my shop site. i try like i say emulate teh same code but does work, i hope get some hand here peoples!
thanks all in advance.