Hi there,
each page or post has a unique ID which can be used.
If you edit a Page you can get the ID from the URL in your browser, if its a Page or a Post it will look like this: post=899
So for his page the CSS would be:
.page-id-899 {
background-image: none;
}
If it was a Post then the CSS would like this:
.postid-899 {
background-image: none;
}