JSFiddle - React, Tailwind, and code Playground

HTML

<section class="comment-block">
    <div class="comment-title">
        ...
        <button class="reply_btn">Reply</button>
        ...                                                                             
    </div>

    <p class="comment">Test comment</p>

    <form method="POST" action="/org/post/{comment_id}" class="reply-form">
        <input name="_method" type="hidden" value="PUT"></input>
        <textarea name="body" cols="50" rows="10"></textarea>
        <div class="button-group">
            <input type="submit" value="Post Comment">Post comment</input>
            <input type="button" class="cancel_btn" value="Cancel"></input>
        </div>
    </form>                                 
</section>

CSS

.reply-form{
    display:none
}

JavaScript

$(function(){
    $(".reply_btn").click(function () {
      $(this).parent().children('.reply-form').show();
    }); 
    $(".cancel_btn").click(function(){
      $(this).parent().hide();
    });
});