Why is the default form not in form of box?

There are 2 versions of the forms. The line and box to fill in information. I'd like to create the box one. The code on the documentation doesn't work.

Code page: https://mdbootstrap.com/components/forms/

<!-- Default form subscription -->
<form>
    <p class="h4 text-center mb-4">Subscribe</p>

    <!-- Default input name -->
    <label for="defaultFormSubscriptionNameEx" class="grey-text">Your name</label>
    <input type="text" id="defaultFormSubscriptionNameEx" class="form-control">
    
    <br>

    <!-- Default input email -->
    <label for="defaultFormSubscriptionEmailEx" class="grey-text">Your email</label>
    <input type="email" id="defaultFormSubscriptionEmailEx" class="form-control">

    <div class="text-center mt-4">
        <button class="btn btn-outline-purple" type="submit">Send<i class="fa fa-paper-plane-o ml-2"></i></button>
    </div>
</form>
<!-- Default form subscription -->