JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/autosize.js/6.0.1/autosize.min.js"></script>
<h1 style="text-align: center;">JavaScript 系列四：第1課 ── autosize 套件</h1>

<form action="" method="post">
  <h1>留言板</h1>
  <label for="username">暱稱</label>
  <input type="text" name="username" id="username" placeholder="暱稱" required>

  <label for="comment">留言</label>
  <textarea name="comment" id="comment" cols="30" rows="3" placeholder="留言" required></textarea>

  <input type="submit" value="送出">
</form>

CSS

* {
  padding: 0;
  margin: 0;
}

form {
  width: 600px;
  margin: 30px auto;
  box-sizing: border-box;
  border: 5px solid #2219a8;
  border-radius: 10px;
  padding: 20px;
  text-align: center;
  font-size: 0;
}

form h1 {
  font-size: 24px;
  font-weight: 900;
  margin-bottom: 20px;
  color: #2219a8;
}

form label,
form input,
form textarea {
  display: inline-block;
  vertical-align: top;
  font-size: 14px;
}

form label {
  font-size: 16px;
  font-weight: 900;
  width: 20%;
  box-sizing: border-box;
  border-left: 3px solid #130e53;
  margin: 20px 0;
  padding: 5px;
  color: #2219a8;
}

form input,
form textarea {
  font-size: 14px;
  width: 80%;
  box-sizing: border-box;
  padding: 5px;
  margin: 20px 0;
}

form textarea {
  line-height: 2;
  resize: none;
  text-align: justify;
}

form input[type="submit"] {
  cursor: pointer;
  border: none;
  border-radius: 10px;
  background-color: #2219a8;
  color: #fff;
  padding: 10px;
  font-size: 16px;
  font-weight: 900;
  transition: 0.3s;
}

form input[type="submit"]:hover {
  background-color: #6058c4;
}

JavaScript

let textarea = document.querySelector("textarea");
autosize(textarea);