The content reveals the footer when you scroll down.

Click "Page Source" in your browser menu to see HTML / CSS.

This only works as full page (on browser window bounds), not as nested component somewhere in a page.
When setting the footer z-index to 3, the footer will be always visible.
When setting the header z-index to 1, the header will disappear when scrolling down.
The margin-top of content must match the footer height, and its margin-bottom the header height.

Content line ...

The header remains visible when you scroll down.

The content reveals the footer when you scroll down.

The footer is revealed when scrolling to page end.