You already have a partly working example on the following line:
var links = upTo(button, "links");
where "links" needs to be changed from an element selector to a class selector, by adding a fullstop in front of the word.
The bad line that you need to fix is:
var button = upTo(evt.target);
where you need to add a second argument which which is the selector that you are looking for. In this case, it's the "playButton" selector.