Tips on Customizing Block Catalog

How to Hide Block Catalog Admin Menus

function plt_hide_block_catalog_menus() {
	//Hide the "Posts → Block Catalog" menu.
	remove_submenu_page('edit.php', 'edit-tags.php?taxonomy=block-catalog');
	//Hide the "Pages → Block Catalog" menu.
	remove_submenu_page('edit.php?post_type=page', 'edit-tags.php?taxonomy=block-catalog&post_type=page');
	//Hide the "Tools → Block Catalog" menu.
	remove_submenu_page('tools.php', 'block-catalog-tools');
}

add_action('admin_menu', 'plt_hide_block_catalog_menus', 11);

Where do I put this code?

How to Hide the "Block Catalog" Meta Box

function plt_hide_block_catalog_metaboxes() {
	$screen = get_current_screen();
	if ( !$screen ) {
		return;
	}

	//Hide the "Block Catalog" meta box.
	remove_meta_box('block-catalogdiv', $screen->id, 'side');
}

add_action('add_meta_boxes', 'plt_hide_block_catalog_metaboxes', 20);