CSS for changing only the backgroudn color on single post.

Dear GP support team,

My name Jinhyung Lee, and I would like to know the CSS code to change only the background color on single post.

http://jungmyungsa.org/%EB%B6%80%EC%B2%98%EC%9D%98-%EB%98%90-%EB%8B%A4%EB%A5%B8-%EA%B3%A0%EB%AF%BC-%EB%B9%97%ED%88%AC/

As you can see the post on my website, there is a light grey background under the content. I want to make all the background white color without any containers.

Please let me know how to do this.
Thank you.

Best,
Jinhyung Lee