Post width shrunk

I was trying to reduce the size of the featured image following the suggestions here in the forum by using the Custom CSS plug-in. It didn’t seem to take, but not a big drama. however, I went to post a new entry, and was startled to find all my posts are centered and extremely narrow. This is an issue, especially since many of my posts are very long articles. I’ve obviously done something wrong in the Custom CSS. Can you help with how I might restore the site back to the original width of my text? My site is: itsgoingok.com