// Featured Thumbnail
function featured_thumbnail() { 
	ob_start(); ?>
	<div class="thumbnail-block">
		<?php $featured_img_url = get_the_post_thumbnail_url( get_the_ID(),'full'); ?>
		<div class="page-thumbnail" style="background-image: url('<?php echo $featured_img_url; ?>');"></div>
	</div>
	<?php return ob_get_clean();
}
add_shortcode ('featured_thumbnail','featured_thumbnail');