ECOM-811 design and layout changes

@wedaly @stephensanchez @rlucioni here are the style and text updates. Unfortunately I had to use teh dreaded !important in my Sass to override some ridiculously specific selectors, but after the A/B test we can clean this up by removing the legacy styles.
This unfortunately is not going to work for i18n.  I don't know a way to interpolate HTML into an underscore template (when I've used `_.sprintf` before the HTML ended up being escaped).