The bar across the top of an app or site, with the name, the main links and actions, staying put as the page scrolls and collapsing its links on phones.
data-sticky keeps it at the top as the page scrolls, with a frosted background. On narrow screens the links scroll sideways in their own strip under the name; for many links, put them in a drawer behind a menu button instead.
Accessibility
As the page's <header>, it's the banner landmark; the links are a nav named "Main". Put a "Skip to content" link first.
The current page's link has aria-current="page", shown with an underline as well as colour.