Royal Technologies on "[Plugin: Royal Custom CSS for Page and Post] CSS Code"

Trying to use this to change the background color of a post. But, none of the CSS codes I have tried work. Can you tell me the css code that I need to use to change the background color of a single post?

https://wordpress.org/plugins/rt-custom-css-page-and-post/

like body color you may use !important

body{background:#7881CF!important;}