As a dependent revision of D19369, this patch adds a circle behind action button icons in order to make sure they are legible.
Oh one more thing: the ActionButton component is also used in the logout screen. Does this look good there too when the background is dark, or does it become kind of muddy?
The way we solved this in the old version was by adding a light-colored outline around the circle to provide contrast when the background is also dark. I'd recommend that we do that here too, or else make the background circle optional and omit it on the logout screen when its background is dark.