Example

<?php
$form = new Form('plugins-modal-form-1', 'vertical');

$form->addInput('text', 'user-name-modal', '', 'username', 'required');
$form->addInput('email', 'user-email-modal', '', 'e-mail address', 'required');
$form->centerContent();
$form->addBtn('button', 'cancel-btn-modal', 1, 'Cancel', 'class=btn btn-default, data-modal-close=modal-target', 'submit_group');
$form->addBtn('submit', 'submit-btn-modal', 1, 'Send ', 'class=btn btn-success', 'submit_group');
$form->printBtnGroup('submit_group');

$modal_options = [
    'title'       => 'Here is a modal form',
    'title-class' => 'text-secondary font-weight-light',
    'title-tag'   => 'h3',
    'animation'   => 'flip-in-horizontal'
];
$form->modal($modal_options);
?>

<div class="text-center">
    <button data-micromodal-trigger="modal-plugins-modal-form-1" class="btn btn-primary text-white btn-lg">Open the modal form</button>
</div>

<div class="bs5-form-stacked-element mb-3">
	<label for="user-name-modal" class="form-label">
		username <sup class="text-danger">* </sup>
	</label>
	<input id="user-name-modal" name="user-name-modal" type="text" value="" required class="form-control">
</div>
<div class="bs5-form-stacked-element mb-3">
	<label for="user-email-modal" class="form-label">
		e-mail address <sup class="text-danger">* </sup>
	</label>
	<input id="user-email-modal" name="user-email-modal" type="email" value="" required class="form-control">
</div>
<div class="mb-3 phpfb-centered">
	<div class="btn-group">
		<button type="button" name="cancel-btn-modal" value="1" class="btn btn-default" data-modal-close="modal-target">
			Cancel
		</button>
		<button type="submit" name="submit-btn-modal" value="1" class="btn btn-success">
			Send 
		</button>
	</div>
</div>