Custom fields for every page
ok let us try this ,,, maybe help

1- add new image field to your content type (background field)

2- open node.tpl.php in your theme

3- test if this node from this content type ,, then get the value of the background field image

4- do some thing to make this image url as a background

do the same with a little bit different for the styles :)

For Specific URL (this way maybe not professional):

1- create new content type (Backgrounds) with two fileds (URL + Image)

2- open page.tpl.php and write some php code can test if the current URL exists in any node from content type (Backgrounds)

3- if yes => get the image field and make it as background