Hmmm… not using that method, as Z-Index is relative to its parent container. So The title can be in front of its own background but not a container that sits outside if it.
Are you just wanting to display just the Post Title?
If so you can use this PHP Snippet to create a shortcode:
function post_title_shortcode(){
return get_the_title();
}
add_shortcode('post_title','post_title_shortcode');
Then you can build the entire thing in the Block editor with this shortcode: [post_title]
Still keep your header element for merging only.
The next version of GPP will have dynamic content built into the Block Editor 🙂