<?php if (has_post_thumbnail( $post->ID ) ): ?>
                <?php $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'single-post-thumbnail' ); ?>

                <div class="slide">
                    <div class="slide_img" style="background-image:url(<?php echo $image[0]; ?> )"></div>
                </div>
                <?php endif; ?>