Style navigation buttons
Style navigation buttons

The specs show that the buttons have a black background and are
themselves 30% opaque, instead of having an alpha(black, 0.2) background.
They also needed slightly less rounded corners.

[endlessm/eos-sdk#2506]

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib