我在一個WordPress網站上工作，需要使用PHP代碼片段來操作HTML。具體來說，我需要添加、替換或更改某個類。我當前的代碼能夠定位特定的文章，但是不能檢索它的CSS類，并且我不能改變它。我如何才能做到這一點？

function add_video_symbol3($containsVideo, $postId) { 

    if ($containsVideo === '1'){    
            
       //replace-method does not work
       //$thumbnail_html_with_class = str_replace('class="thumbnail-link', 'class="thumbnail-link video_post_play-button-overlay', $thumbnail_html);         
    
    return  $containsVideo;
      }
    }
add_filter('post_thumbnail_html', 'add_video_symbol', 10, 2);

// Set up the query to retrieve all posts
$args = array(
     'post_type' => 'post',  // Replace with your post type if necessary
     'posts_per_page' => -1, // Retrieve all posts
    );
$query = new WP_Query($args);

// Check if there are any posts
if ($query->have_posts()) {
    // Loop through each post
    while ($query->have_posts()) {
        $query->the_post();
       
        // Get the value of a specific custom field (e.g., 'contains_video')
        $containsVideo = get_post_meta(get_the_ID(), 'contains_video', true);
        $postId = get_the_ID();
        
        $filter_val = apply_filters('post_thumbnail_html', $containsVideo, $postId);
    }
    // Restore the global post data
    wp_reset_postdata();
} else {
    echo 'No posts found';
}