How do I make the text in a text box disappear when I click on it?

[admin]

The part that says "Get notified when its ready via email" is the text in question. I am using the WP Maintenance Mode plugin <a href="https://wordpress.org/plugins/wp-maintenance-mode/" rel="nofollow">https://wordpress.org/plugins/wp-maintenance-mode/</a> for this page on my Wordpress site. You can see the text box on my website <a href="http://boasish.com" rel="nofollow">http://boasish.com</a>.

<div class="subscribe_wrapper" style="min-height: 100px;">
  <form class="subscribe_form" novalidate="novalidate">
    <input type="text" placeholder="Get notified when it is ready via email" name="email" class="email_input" data-rule-required="true" data-rule-email="true" aria-required="true">
    <input type="submit" value="Submit">
  </form>
</div>

<pre class="lang-css prettyprint-override">

.wrap form.subscribe_form input[type="text"] {
  text-align: center;
  font-family: 'Myriad Pro';
  height:42px
  padding: 11px 10px 10px 0;
  width: 388px;
  padding-top: 16px
}