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.
The original string is better for i18n, fwiw. What follows the colon? If possible, please put whatever follows the colon into the i18n string. If not possible, please add a translators comment explaining what follows the colon.