delete border around content box twenty twelve

I am working on a client landing page and have set the page with css code but I can’t figure out how to get the thin gray border gone from the content area of a page. I have been able to get rid of all of the other borders on the page except this one.

Here is the link to the site so you can see what I am talking about – editing css in Jetpack->appearance->css editor

https://simplythebestbrandingworkshop.com/