How to have css background image scale with window size and device

Question

I am trying to setup a fluid template that I can use for responsive design viewports too. However now when I try to resize my browser window it does not scale and on my iphone i just see the top left part of my header graphic. I have a main wrapper background and a header animated gif that are both the same width of 1200px. Any help would be greatly appreciated.

viewport

<meta name="viewport" content="width=device-width, initial-scale=1">

css

body {
    background-color: #B28D66;
    margin: 0 auto;
}
#Wrapper {
    max-width:1200px;
    width:95%;
    background-image: url(../img/background_main.jpg);
    background-repeat: no-repeat scroll;
    background-position: center top;
    height: 2200px;
    position: relative;
    margin-top: 0;
    margin-right: auto;
    margin-bottom: 0;
    margin-left: auto;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}
#Wrapper #Banner {
    width: 100%;
    height: 350px;
    background-image: url(../img/animated-gif-header.gif);
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}
#Wrapper #Content {
    width: 75%;
    margin: 0 auto;
}
#Wrapper #MainNav {
    background-image: url(../img/nav_bar.png);
    width: 100%;
    height: 75px;
    margin-top: -20px;
}
#Wrapper #MainNav ul {
    margin-right: 100px;

}

#Wrapper #MainNav ul li {
    float: right;
    margin-top: 15px;
    padding-right: 21px;

Answer 1

background-image: url('');
background: no-repeat center center cover;

This usually works fine.

Answer 2

try using the background-size property in the following manner:

background-size:100% auto;

or use the below if you want to have its height covering the whole page height

background-size:auto 100%;

Answer 3

background-size: cover;

works just fine for me.