How to create a CSS input field for AMP

amp_css.php

// AMP 用 CSS の入力欄
add_action( 'amp_post_template_css', 'xyz_amp_my_additional_css_styles' );
function xyz_amp_my_additional_css_styles( $amp_template ) {
?>
/* CSS の追加は以下に */



/* CSS の追加はこの上に */
<?php
}