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>