JSFiddle - React, Tailwind, and code Playground

HTML

<form id="comments-form">
    <div>Ответ:</div>
    <textarea></textarea>
</form>

<ul>
    <li>
        <p>Lorem ipsum dolor</p>
        <button>Ответить</button>
    </li>
    <li>
        <p>Lorem ipsum dolor</p>
        <button>Ответить</button>
    </li>
    <li>
        <button>Ответить</button>
    </li>
<ul>

CSS

#comments-form {
    border: #ddd 1px solid;
    width: 200px;
    padding: 5px;
    display: none;
}
ul {
    margin: 0;
    padding: 0;
}
li {
    border: #ddd 1px solid;
    padding: 5px;
    margin: 5px 0;
    list-style: none;
}

JavaScript

var $form = $('#comments-form');

$('button').on('click', function () {
    $(this).closest('li').append(
        $form.show()
    );
    
    return false;
});