Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, function "wp_load_classic_theme_block_styles_on_demand" not found or invalid function name in /wp-includes/class-wp-hook.php:341 Stack trace: #0 /wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters(NULL, Array) #1 /wp-includes/plugin.php(522): WP_Hook->do_action(Array) #2 /wp-settings.php(742): do_action('init') #3 /wp-config.php(92): require_once('/wp-settings.ph...') #4 /wp-load.php(50): require_once('/wp-config.php') #5 /wp-blog-header.php(13): require_once('/wp-load.php') #6 /index.php(17): require('/wp-blog-header...') #7 {main} thrown in /wp-includes/class-wp-hook.php on line 341