WordPress Instant Articles - Hint about subresources to load from a WordPress theme or child theme - https://wordpress.org/plugins/instant-articles/

theme-subresource.php

<?php
add_filter('wpinstant_subresources', function($subresources) {

    //Will add link rel="subresource" for /style.css and /js/main.js in the theme folder.
    $subresources[] = get_stylesheet_directory_uri() . '/style.css';
    $subresources[] = get_stylesheet_directory_uri() . '/js/main.js';

    return $subresources;
});