- it works only with multipage scores (well, on an inlined score image the extra spacing is not expected, but if the midi player is added the spacing is still needed)
- it adds extra space not only before the player, but also between pages (well, in most cases it does not hurt, but see below)
- the space is in em (current context font-size dependant). And this can sometimes give unexpcted results.
I would suggest the extra space to be in px, added only after the last page and only if the player is present.
Maybe just put the player into an extra div with non-zero margin-top?