<?php
// In der functions.php einbinden

add_action('admin_bar_menu', function ($admin_bar) {
	if (!is_admin() && WP_DEBUG) $admin_bar->add_menu([
		'id'    => 'my-item',
		'title' => 'Breakpoint: ' .
			'<strong class="d-sm-none">XS</strong>' .
			'<strong class="d-none d-sm-inline d-md-none">SM</strong>' .
			'<strong class="d-none d-md-inline d-lg-none">MD</strong>' .
			'<strong class="d-none d-lg-inline d-xl-none">LG</strong>' .
			'<strong class="d-none d-xl-inline">XL</strong>'
	]);
}, 1000);