Inline CSS Featured Image Set Up With WP Query Loop

<?php
  $loop = new WP_Query(array('post_type' => 'slider-items', 'order' => 'DESC','posts_per_page' => 5));
?>
<?php while($loop->have_posts()) : $loop -> the_post(); ?>
     <div class="item">
            <div class="single-slider" style="background-image: url('<?php echo wp_get_attachment_url( get_post_thumbnail_id() ); ?>')">
                    <div class="slide-item-table">
                        <div class="slide-item-tablecell">
                            <div class="container">
                                <div class="row">
                                    <h2><?php the_title(); ?></h2>
                                    <?php the_content(); ?>
                                    <a href="#rooms" class="btn-filled smooth-scroll">Book A Room</a>
                                    <a href="#contact" class="btn-filled btn-gold smooth-scroll">contact us</a>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
<?php endwhile; ?>