Customizing Comment Forms

I am trying to customize the comment form, which you can see here – https://rachelchaikof.com/testing/hello-world/#comment-1

I am obviously using WordPress 3.0 comment code – <?php comment_form(); ?>

With this code alone, how can I create borders with colors, choose border thickness, color of text, and all that CSS styling? Is there a good tutorial on how to design the comment form with this code alone?