Style WP Admin top bar more consistently with Calypso top bar

[manospsyx]

Now that WP Admin is the default for new Woo Express sites, the WP Admin top bar has replaced the Jetpack bar, and lost some of the styling customizations that made it consistent with Calypso.

Until we completely remove Calypso, and for styling consistency between WP Admin and Calypso areas, it might be a good idea to slightly update the WP Admin bar design: