Adjusting content width?

Hey, I've recently found Grav and started working on a website/blog. Slowly getting the hang of everything. One thing I haven't been able to do is change the content width on pages. I use the regular Antimatter theme and especially with longer blocks of text the text gets very tiresome to read since it spreads so wide. Would anyone be able to tell me what changes do I need to make in the Twig-files to make paragraphs more narrow?

I have a custom.css file but I haven't figured out what I would need to change on the .html.twig files to call for the CSS changes. I have multiple pages on my site, I would like to apply the change on all of them.

You could apply padding around the text? That would contain the text within a smaller space.

Ah, yes, I considered that, I was just afraid it could cause further issues with different screen-sizes so I was wondering if there would be a more elegant solution, but maybe that's just me making things more complicated than they need to be. Thanks lewissn!

Padding will apply within the specified element, and only affect overall size insofar as the element has a declared width. As I recall Antimatter does not use such declared widths on lower-level elements, so adding/increasing padding will not affect different screen-sizes but only constrain the content itself.