This theme has a versatile header that can be fixed, animated on scroll, transparent (over images and backgrounds) and inverted. By default the header is fixed and will animate on scroll.
# config.toml
 [params.global]
    header_fixed = true
As long as the header has the class header-fixed or header_fixed = true is enabled in the config.toml it will animate on scroll, changing the background from transparent to white and adding a boxshadow.