Stratus - Header & Footer Options Overview
In the Stratus theme, there are two separate options for the site header (and footer). There is the standard default theme header, and the new Elementor header / footer builder within the Global Templates area.
1) In the standard default header, it can be set to an opaque white or dark grey background site-wide, and on a per-page basis it can be set to a transparent background with the option of either white or dark content. All of the core theme options (Appearance > Customize > Theme Options > Menu & Header) apply only to the default header.
2) Then there is the newer Elementor header / footer builder which allows for much more customization and flexibility. If enabled, it replaces the default theme header. We include templates for the examples shown in the live demo as well.
See here for more info on the Global Templates header / footer builder.