Current Harmony close buttons are 24 DIP per side (since they are VectorIconButtons, and all such buttons are 24 DIP).  The spec says to use 16.

Open questions for Alan:
* Should other such icon buttons also be 16?  For example, the find next/previous "arrow" buttons in the find box.  My patch to fix this changes these as well.  This seems likely correct to me (it would be weird to have three icons in a row, but the third has a smaller target), but I'm a little leery of the sort of fixed-size assumptions I'm seeing in the code.

* Playing with these close buttons for only a few minutes, the hover targets feel *really* small at 16 px.  I'm worried about a11y here in particular.  Compare to e.g. Windows native where window close button targets are humongous (~45x29 on Win 10), we're going from something that's about 1/2 the window close button area to something that's about 1/5th the close button area.  It feels a little tricky to target to me.  How much practical testing have we already done here to feel confident of this choice?  What sort of testing/considerations should we give as/after we land, to make sure we stay happy with it?