Extra body class

addbodyclass.php

<?php

function mimified_ads($classes) {
    $categories = get_the_category();
    if(is_single()){
      if(!in_array($categories[0] -> term_id, array(68,69,71,50))){
        $classes[] = 'trending-post';
      }
    }
    return $classes; 
}

add_filter('body_class', 'mimified_ads');