For example, click the small view (right-most size option) to hide everything. I would expect that the downward-facing arrow expands an individual topic. Commonly, down expands (then the arrow transforms to an up arrow) and up contracts again.
However, the down arrow actually seems to be a dropdown menu. Perhaps a triple line icon (or other menu indicator) can be used instead.
Version: master
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=58661
https://bugzilla.wikimedia.org/show_bug.cgi?id=57696