Hello there,
Thanks for reaching us, We will surely resolve your issue.
Whenever this form is submitted, this function is called, route is defined here
And with the help of view_render_event you will be able to add your custom html means if you want to add css in anothers package's view file you can do it with the help of this event.
Let me know if you have any further query. We are here to help you.
Thanks !