JSFiddle - React, Tailwind, and code Playground

HTML

<textarea aria-required="true" required="required" name="40d42-comment" placeholder="Dein Kommentar" id="comment"></textarea>
<input id="submit" type="submit" value="Kommentar abschicken" name="submit">

CSS

#comment:invalid {
    height: 75px;
}

#comment:valid ,#comment:focus {
    height: 375px;
}