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.
@rlucioni  and @AlasdairSwan I'll attach final copy to the ticket today. Renzo is right: that use of "Register" is incorrect; it should be Enroll. I'll review the comps with Marketing and get it settled today.