Background Manager and Responsive

Hi
I am using background manager and I am having trouble re sizing the background image on smaller screens. For example, I am using this css:

/* =Start From Here
-------------------------------------------------------------- */
body {
background-image: url('http://buildawebsite.ie/wp/wp-content/uploads/2013/02/ratas-12.png') !important;
background-position: top right !important;
background-color: #4b99e8 !important;
background-size: 45%;
}

and this works fine on fullscreeen but when I want to resize the image on smaller screens I’m using this code further down the stylesheet and it doesn’t work:

@media screen and (max-width: 650px) {

body {
background-image: url('http://buildawebsite.ie/wp/wp-content/uploads/2013/02/ratas-12.png') !important;
background-position: top right !important;
background-color: #4b99e8 !important;
background-size: 5%;
}

where am I going wrong? Thanks

http://wordpress.org/extend/plugins/background-manager/