Find out div class

CSS classes in plugins come straight from the plugins. It’s safer to add CSS to a child theme (or your current theme’s “Custom CSS” area if it has one) targeting the plugin’s class. If you edit the plugin files, anytime you update the plugin, your changes will be overwritten.

Please note, the Edit Theme functionality is also rather insecure and is best turned off. It too suffers from the same issue – if you make changes directly and then update your theme, your changes are lost. (And it’s important to keep plugins and themes up to date as updates often contain security patches.)