Example

$form = new Form('plugins-ladda-form-1', 'vertical');

$form->centerContent();

$form->startFieldset('expand-left', 'class=bg-gray-100 mb-5', 'class=small text-center py-2 mb-3 bg-gray-200');
$form->addBtn('button', 'my-btn-1', 1, 'Send <span class="bi bi-envelope ms-2"></span>', 'class=btn btn-secondary, data-ladda-button=true, data-style=expand-left');
$form->endFieldset();

$form->startFieldset('contract', 'class=bg-gray-100 mb-5', 'class=small text-center py-2 mb-3 bg-gray-200');
$form->addBtn('button', 'my-btn-2', 1, 'Send <span class="bi bi-envelope ms-2"></span>', 'class=btn btn-secondary, data-ladda-button=true, data-style=contract');
$form->endFieldset();

$form->startFieldset('contract-overlay', 'class=bg-gray-100 mb-5', 'class=small text-center py-2 mb-3 bg-gray-200');
$form->addBtn('button', 'my-btn-3', 1, 'Send <span class="bi bi-envelope ms-2"></span>', 'class=btn btn-secondary, data-ladda-button=true, data-style=contract-overlay');
$form->endFieldset();

$form->startFieldset('zoom-in', 'class=bg-gray-100 mb-5', 'class=small text-center py-2 mb-3 bg-gray-200');
$form->addBtn('button', 'my-btn-4', 1, 'Send <span class="bi bi-envelope ms-2"></span>', 'class=btn btn-secondary, data-ladda-button=true, data-style=zoom-in');
$form->endFieldset();

$form->startFieldset('slide-left', 'class=bg-gray-100 mb-5', 'class=small text-center py-2 mb-3 bg-gray-200');
$form->addBtn('button', 'my-btn-5', 1, 'Send <span class="bi bi-envelope ms-2"></span>', 'class=btn btn-secondary, data-ladda-button=true, data-style=slide-left');

$form->startFieldset('data-spinner-color=darkmagenta, data-spinner-lines=6', 'class=bg-gray-100 mb-5', 'class=small text-center py-2 mb-3 bg-gray-200');
$form->addBtn('button', 'my-btn-6', 1, 'Send <span class="bi bi-envelope ms-2"></span>', 'class=btn btn-secondary, data-ladda-button=true, data-spinner-color=darkmagenta, data-spinner-lines=6');
$form->endFieldset();

Your copy of PHP Form Builder is NOT authorized.
About PHP Form Builder License

expand-left
contract
contract-overlay
zoom-in
slide-left
data-spinner-color=darkmagenta, data-spinner-lines=6
<fieldset class="bg-gray-100 mb-5">
	<legend class="small text-center py-2 mb-3 bg-gray-200">
		expand-left
	</legend>
	<div class="mb-3 phpfb-centered">
		<button type="button" name="my-btn-1" value="1" class="btn btn-secondary" data-ladda-button="true" data-style="expand-left">
			Send <span class="bi bi-envelope ms-2"></span>
		</button>
	</div>
</fieldset>
<fieldset class="bg-gray-100 mb-5">
	<legend class="small text-center py-2 mb-3 bg-gray-200">
		contract
	</legend>
	<div class="mb-3 phpfb-centered">
		<button type="button" name="my-btn-2" value="1" class="btn btn-secondary" data-ladda-button="true" data-style="contract">
			Send <span class="bi bi-envelope ms-2"></span>
		</button>
	</div>
</fieldset>
<fieldset class="bg-gray-100 mb-5">
	<legend class="small text-center py-2 mb-3 bg-gray-200">
		contract-overlay
	</legend>
	<div class="mb-3 phpfb-centered">
		<button type="button" name="my-btn-3" value="1" class="btn btn-secondary" data-ladda-button="true" data-style="contract-overlay">
			Send <span class="bi bi-envelope ms-2"></span>
		</button>
	</div>
</fieldset>
<fieldset class="bg-gray-100 mb-5">
	<legend class="small text-center py-2 mb-3 bg-gray-200">
		zoom-in
	</legend>
	<div class="mb-3 phpfb-centered">
		<button type="button" name="my-btn-4" value="1" class="btn btn-secondary" data-ladda-button="true" data-style="zoom-in">
			Send <span class="bi bi-envelope ms-2"></span>
		</button>
	</div>
</fieldset>
<fieldset class="bg-gray-100 mb-5">
	<legend class="small text-center py-2 mb-3 bg-gray-200">
		slide-left
	</legend>
	<div class="mb-3 phpfb-centered">
		<button type="button" name="my-btn-5" value="1" class="btn btn-secondary" data-ladda-button="true" data-style="slide-left">
			Send <span class="bi bi-envelope ms-2"></span>
		</button>
	</div>
	<fieldset class="bg-gray-100 mb-5">
		<legend class="small text-center py-2 mb-3 bg-gray-200">
			data-spinner-color=darkmagenta, data-spinner-lines=6
		</legend>
		<div class="mb-3 phpfb-centered">
			<button type="button" name="my-btn-6" value="1" class="btn btn-secondary" data-ladda-button="true" data-spinner-color="darkmagenta" data-spinner-lines="6">
				Send <span class="bi bi-envelope ms-2"></span>
			</button>
		</div>
	</fieldset>