FirstScreenLabel.php

<?php
/**
 * @file
 * Contains \Drupal\pureworld\Plugin\Setting\Pureworld\FirstScreen.
 */

namespace Drupal\pureworld\Plugin\Setting\Pureworld\FirstScreen;

use Drupal\bootstrap\Plugin\Setting\SettingBase;


/**
 * The "pwt_first_screen_label" theme setting.
 *
 * @ingroup plugins_setting
 *
 * @BootstrapSetting(
 *   id = "pwt_first_screen_label",
 *   type = "textfield",
 *   title = @Translation("First screen label"),
 *   defaultValue = "Why us?",
 *   description = @Translation("First screen label value."),
 *   groups = {
 *     "pureworld" = @Translation("Pureworld"),
 *     "firstscreen" = @Translation("First Screen"),
 *   },
 * )
 */
class FirstScreenLabel extends SettingBase {

}

<div class="col-md-12 f-screen-label"><h3 class="text-center"> {{ theme.settings.pwt_first_screen_label|trans }} </h3></div>