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.
Our standard is one space, I believe. @AlasdairSwan throughout this PR, you put two spaces between sentences. I would change to 1.

And yes, you need to abstract out `platform_name`.