The Post tab allows you to enable and set the background color of your website's body, as well as adjust the width of the post content.
1. Log into your Blogger dashboard.
2. Go to Theme > Customize > Advanced > Post.
3. Make necessary changes > Save.
Wide content: Adjusts the width of the entry content.
Enable to add background color to the body of the publication page:
Enable Post body background:
To disable: Value 0px to disable.
To enable: Value 1px to enable.
Post body background: Choose the background color to the body of the post page: