Here is the CSS file used by Jetpack displayed in an easier to read format. The CSS file in Jetpack and been minimized to take up less space. Sometimes you will want to override the default CSS used in the various Jetpack modules. All you have to do is scroll down and find the CSS rule you need to modify, copy it, and then paste it into your theme’s stylesheet (or your theme’s child theme’s CSS). You can then modify it.
If you don’t want to modify your theme’s stylesheet, I recommend Simple CSS. It’s the one plugin I install on every WordPress site I create or work on. Unlike the built-in Additional CSS found in the WordPress Customizer, Simple CSS allows you to easily modify the CSS for individual posts and pages. It’s great!