Set different background images for different category posts(not archive pages)

Greetings to all members, I have been trying to get a fix around this issue and certainly could not find any so have decided to post the detailed issue on the forum.

ISSUE: I want to have different background images loaded with different categories and their posts included. For example: Category 1 has “A” background image so this image should also be the background image for all the posts in category 1

What I could do until now : using the “Body_class()” in the header and the following code in css, I am able to manage and change background images for the post archives page of the following categories, but the background goes blank as I get into the categories posts.

Example of the CSS code used :

body.home {
background-image: url('images/braincloseup4.jpg');
}

body.category-robot{
    background-image: url('images/oldpaper2.jpg');
}

body.category-space{
    background-image: url('images/oldpaper3.jpg');
}

body.category-brain{
    background-image: url('images/braincloseup4.jpg');
}

Any help on this issue would certainly be appreciated.
Thanks