添加缩略图/特色图片和摘录以循环播放（多站点）

Question

我尝试了一些不同的操作，但被卡住了。
我想在循环中添加缩略图/特色图像。如果可能的话，网站摘录也要
。
这是我所拥有的：

function subsites_list_sites() {
    $subsites = get_sites();
    $returnHtml = '';    
    if ( ! empty ( $subsites ) ) {  
        $returnHtml .= '<div class="subsites-container">';
        foreach( $subsites as $subsite ) {

            $subsite_id = get_object_vars( $subsite )["blog_id"];
            $subsite_name = get_blog_details( $subsite_id )->blogname;
            $subsite_link = get_blog_details( $subsite_id )->siteurl;

            $returnHtml .= '
            <div class="subsite-item site-' . $subsite_id . '">
                <div class="thumb"><a href="' . $subsite_link . '">Here i want the featured image/thumbnail to display</a></div>
                <div class="wrapper">
                    <div class="title">
                        <a href="' . $subsite_link . '"><h3 class="title">' . $subsite_name . '</h3></a>
                    </div>
                    <div class="content">
                        <a class="excerpt" href="' . $subsite_link . '"><p>Here i want excerpt<p></a>
                        <a class="btn-link" href="' . $subsite_link . '">GO TO WEBSITE</a>
                    </div>
                </div>
            </div>';
        }
        $returnHtml .= '</div>';
    }
    return $returnHtml;
}
add_shortcode( 'subsites_list_sites_sc', 'subsites_list_sites' );