Add a Class Name to the 1st Post in the WordPress Loop

<?php         
$args = array( 'post_type' => 'post', 'posts_per_page' => -1, "order" => "DESC");
$query = new WP_Query( $args );

if ( $query->have_posts() ) {
$i=0;
while ( $query->have_posts() ) { 
$query->the_post();?>
            <!-- Slide One - Set the background image for this slide in the line below -->
            <div class="item <?php echo ($i==0)?'active':''; ?>" style="background-image: url('<?php echo get_post_meta(get_the_id(),'s_image', true);?>');">
                <div class="carousel-caption d-none d-md-block">
                    <!-- <h3>Truck Loan Hub Centre</h3>
            <p>Call us to get the best auto service in Calgary.</p>-->
                </div>
            </div>
           <?php $i++ ;  }
                            }?>
<?php wp_reset_query(); wp_reset_postdata(); ?>