JSFiddle - React, Tailwind, and code Playground

HTML

<div id="contact_form">
          <form name="contact" method="post" action="">

            <input type="text" name="name" id="name" size="30" value="Name" class="text-input" />
            <label class="error" for="name" id="name_error">Please enter your name.</label>
            <br />

            <input type="text" name="email" id="email" size="30" value="Email" class="text-input" />
            <label class="error" for="email" id="email_error">I need your email.</label>
            <br />

            <textarea rows="10" cols="30" type="textarea" name="message" id="message" value="Message" class="text-input" ></textarea>
            <label class="error" for="message" id="message_error">A message is required.</label>

            <br />
            <input type="submit" name="submit" class="button" id="submit" value="Send" />

          </form>
</div>

<div id="details">
    <p>some details here, not sure what yet</p>
    </div>

<div id="mail_list">
    <input type="text" id="mail" value="Your email" name="mail_list" /><input type="submit" name="submit" class="button" id="submit" value="Send" />
    </div>

JavaScript

$(function() {                                       // <== Doc Ready
    $("#email").change(function() {                  // When the email is changed
        $('#mail').val(this.value);                  // copy it over to the mail
    });
});