I don’t know specifically for the body, but you’ll have to isolate that element. It might be as simple as styling the <p> element.
The CSS guide is here: CSS snippets - Obsidian Help I can’t quickly find anything specific to <p> or regular text.
This is the first potential result I found, but the CSS did change quite a bit for version 1.0. How to adjust the line height with CSS? - #6 by GLight This links is just to show that there are some structured variables you can use to point at different elements, and Reading View vs. Editing View, etc.