If we can break apart the default themes into Horizon and Bootstrap
changes, then we can start to move some of the more theme specific
styles out of Horizon base CSS and into default/horizon/_styles.scss
in order to make the theming more robust.
Partially-Implements: blueprint horizon-theme-css-reorg
Change-Id: Idfe749a2e576da929c4feb3599f5490456173210
7a4e0b3b14