Content lost on reflow (reflow-visibility)
Ensure that no essential content disappears when the viewport is resized or zoomed (e.g., to 320 px width or 256 px height equivalent).
Sticky header blocks content:
A large sticky header remains fixed and covers a significant portion of the viewport at small heights/zoom. As you scroll and tab, parts of the page content and the visible focus can be hidden behind the header.
Reduce the browser window height or zoom in to ~400%. Notice how much of the content area is covered by the header.
Keyboard focus may move behind the sticky header and become invisible.
Important information can be hidden until you scroll past the header.
Focusable link 1