Align Bottom

I have some PNG logos of differing heights that I need to display over a background image (one image per page). Regardless of PNG height, I need to uniformly align them with the bottom of a bloc, but when I assign a class to this floating title art and set a bottom margin, the bottom margin is ignored. Naturally, if I set a top margin, the taller logos force the block to be taller.

A cheap workaround is to make each PNG the same height with the art aligned to the bottom but the extra transparent space would slow down the loading.

What must I do to force Blocs to recognize a bottom margin setting?