Remove Sidebar CSS Class from a Custom Post Type in WordPress

When you need to remove the sidebar completely for a Custom Post Type (CPT) in WordPress. First you need to locate or create your template file and remove the call to get_sidebar(). However this can leave you with an empty space where the sidebar use to be. This is because of the CSS class sidebar on your body element. Removing this can be done by adding the following to your theme’s functions.php file.

function alterBodyClasses($classes)
{
    // Check if this page is our CPT e.g. Book
    if (is_singular('book')) {
        if (($key = array_search('sidebar', $classes)) !== false) {
            // Either replace with the opposite CSS class
            $classes[$key] = 'no-sidebar';
            // OR unset the class completely
            // unset($classes[$key]);
        }
    }

    return $classes;
}
add_filter('body_class', [$this, 'alterClasses'], 99);