page formatting

How do I set the margins of a page to restrict where text can appear? (in the body; not header; not footer) I’ve installed a child theme successfully which uses style.css to modify some aspects of page display. I am not using the blog aspect of WordPress, just “static” pages. I tried reading about template files, but so far nothing has been read about page formatting in particular. Can I invoke margins from my child theme’s style.css? I do not know php.

Thanks.