To clarify, you just want to remove the “border” from the about us page? If so, can you revert the Container Width to its previous value? There’s a refresh icon there if you want to set it back to the default value.
Also, to be sure, can you take a screenshot of the border you’re referring to?
https://postimg.cc/xXw2ZbZ5 Here is the link to my page with the border around it. I would like to remove it from all pages and post please. How do you do it with CSS?
To clarify, do you want all pages and posts to be full width? Or just remove the Off-white “border”.
If you just want to remove the Off-white “border”, you can do so by selecting an identical color for your Body Background in Appearance > Customize > Colors > Body > Background, similar to the Content Background color.