Comments styling

Google is your friend
https://www.darrenhoyt.com/2007/08/18/styling-your-wordpress-comments/
https://5thirtyone.com/archives/774
https://cdharrison.com/2008/12/threaded-comments/

If your theme uses wp_list_comments, the only thing you need to do is add the classes in your stylesheet…

You can get these by checking the source of the page…

Examples:

.bypostauthor {}
.odd {}
.alt {}

and so on…

The above links will help, this one to.
https://www.kremalicious.com/2008/12/howto-styling-author-comments-with-wordpress-27/

You can take this a step further and create a custom callback for the wp_list_comments() function, then add you own classes, i can expand on this if you wish to know more, or just click here.