As you may have seen throughout the demo, there are pages that have different masthead layout, page colors etc. These settings can be adjusted per individual page. For example, you can mix both dark & light portfolio pages on your website.
When editing page with Elementor, click on the very left bottom Cogs icon. Here you will find available document options.
As you can see on the screenshot above there are some project properties. Those are the additional fields editable from admin panel.
If you don’t see those fields, please make sure you have Advanced Custom Fields PRO plugin installed and activated. It’s bundled with theme and don’t need to be purchased separately.