Add expander signal

[Aphexus]

In Kiwix JS and the wikipedia zim when clicking on a section (such as Examples) it hides the content but there is no way of knowing it does this or not since everything looks the same. [One might be able to tell that the next line is that of a new section but it is not so obvious]

E.g., having a simple expander indication like a down arrow or when unexpanded some text that says "expand" would be helpful.