Hi there,
Please kindly consider that in order to some of the elements work correctly in the Cornerstone it is impossible to not load JS of the Cornerstone in none blocking way. In some cases, our elements are dependent to JS to render heavily and it is not possible to have them loaded at the end.
Regarding the CSS we use the standard WordPress way to add the CSS code and it is rather complicated process to determine which CSS should be added. Here is the file path which does that:
wp-content/themes/x/framework/functions/global/enqueue/styles.php
Such customization is outside of our support scope. You will need to use the wp_enqueue_styles function:
https://developer.wordpress.org/reference/functions/wp_enqueue_style/
Thank you for your understanding.