Page Layout Change?

I noticed that this site has started to show up with a smaller width on the screen. It should be full width. I am not sure if it was due to some recent plugin updates or not. This is a site I took over and it had a custom theme. I would like some guidance on where to locate the stylings. For example, if you inspect the home page, you will see that there is a max-width property on the body tag. I am having troble locating that styling. Please advise.