$wpdb->insertでAUTO_INCREMENTの数値型id番号を挿入する

global $wpdb;
$poststable = $wpdb->prefix. 'posts';
$datetime = current_time( 'mysql' );
$gmttime = current_time( 'mysql', true );//第２引数のデフォルトはfalse(日本時間)。trueでgmt時間
$css = '.modal { display: none; } a[data-micromodal-trigger], button[data-micromodal-trigger] { pointer-events: none; opacity: 0.5; }';
$theme = get_stylesheet();

$data = array(
	'ID' => '',//auto_incrimentで%dでも''で連番処理してくれる
	'post_author' => 1,
	'post_date' => $datetime,
	'post_date_gmt' => $gmttime,
	'post_content' => $css,
	'post_title' => $theme,
	'post_excerpt' => '',
	'post_status' => 'publish',
	'comment_status' => 'closed',
	'ping_status' => 'closed',
	'post_password' => '',
	'post_name' => $theme,
	'to_ping' => '',
	'pinged' => '',
	'post_modified' => $datetime,
	'post_modified_gmt' => $gmttime,
	'post_content_filtered' => '',
	'post_parent' => 0,
	'guid' => home_url( '/'. $theme. '/' ),
	'menu_order' => 0,
	'post_type' => 'custom_css',
	'post_mime_type' => '',
	'comment_count' => 0,
);

$format = array(
	'%d', //ID
	'%d', //post_author
	'%s', //post_date
	'%s', //post_date_gmt
	'%s', //post_content
	'%s', //post_title
	'%s', //post_excerpt
	'%s', //post_status
	'%s', //comment_status
	'%s', //ping_status
	'%s', //post_password
	'%s', //post_name
	'%s', //to_ping
	'%s', //pinged
	'%s', //post_modified
	'%s', //post_modified_gmt
	'%s', //post_content_filtered
	'%d', //post_parent
	'%s', //guid
	'%d', //menu_order
	'%s', //post_type
	'%s', //post_mime_type
	'%d', //comment_count
);

$wpdb->insert( $poststable, $data, $format );