Transient header bar
In some cases it would be desirable to hide the header bar, and show more content below it. Ideally the header bar would slide out to the top, and slide back in from the top when it's shown again.
Example use cases:
- Distraction free writing apps (https://github.com/UberWriter/uberwriter/issues/101)
- Video players (e.g. Quicktime on macOS does this)
- Hiding the header when scrolling down is popular on websites and mobile apps (e.g. https://wicky.nillia.ms/headroom.js)
As far as I understand this is currently not possible in a clean way because header bar and content are completely separate areas which do not overlap, but I heard there's interest in changing that for GTK4.