I'm trying to figure out how to mimic a certain behavior I have a screenshot of:

[![](https://i.stack.imgur.com/oNWQe.png)](https://i.stack.imgur.com/oNWQe.png)

How are the curves labeled like that? I initially thought it used the `legend` function, but now I suspect it might not be, considering I haven't found any documentation for it that specifies this behavior.

Bonus: How do you specify the centered labels for each of the `fill` functions here?