My plugin gets a list of the CSS and JS which are queued via wp_enqueue_script() and wp_enqueue_style().
And it sends link: response header which enables to pre-load those resources like following.
Link: ..., </wp-content/themes/example/style.css>; rel=preload; as=style, ...
https://miya.io/2018/03/10/http-2-server-push-plugin-for-wordpress/