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.
I'm also surprised by this. @andywaldrop did note that the copy in his comps isn't necessarily indicative of the final copy we're being asked to use; maybe this is an old string that found its way into the design? If this isn't the case and this is the final copy from marketing, we should bring this up with Griff. We've done a good job recently of separating the meanings of "enroll" and "register," and it seems like conflating these terms again would be a step backwards when it comes to our marketing efforts.