You gave me the kick in the butt needed to improve this functionality.
Until the next version is released, do this:
1. Replace the code in wp-content/plugins/gp-premium/addons/generate-page-header/inc/js/parallax.js
with this: https://gist.github.com/generatepress/923dfa600cc99a4b96e2
If you’re using the standalone Page Header add-on, you’ll find it in: wp-content/plugins/generate-page-header/inc/js
2. Then add this CSS:
.fullscreen-enabled {
display: table;
width: 100%;
}
.vertical-center-enabled {
display: table-cell;
vertical-align: middle;
}
You’ll be able to remove the above CSS once the next version comes out.
Let me know how it goes 🙂