Add class to Reply button in Comments area

Under each comment there is a link called ‘Reply’. I want to add a class to this link. It’s default class is comment-reply-link. How can I do so? I am creating my own theme and I don’t want to manually edit files inside the wp-includes directory.

In your comments.php template file use wp_list_comments and set the parameter callback to your defined function that will generate the template. Inside the function you can style the comment reply link.

wp_list_comments codex
Further reading on comment display