excuse my ignorance

i’m sure this has been asked before but i’m brand NEW to css and wp and everything. all i know is the very basics of how to change text size, etc. but I was wondering what exact element of my wp-layout.css file (it’s the original) do i alter to make my journal not take up the entire page? Like on this site for example, there’s edges. anyways here’s my site https://www.gladlybeyond.bizarre-host.com/wp/
i would just go to one of the css guides and read it, but i don’t know what words to use to describe what i’m talking about other than tables (that css doesn’t have).