CSS Rewrite

I reworked the CSS entirely. Unfortunately this meant I had to change some of the HTML layouts at points to make things as simple as possible. This means that it would have been difficult to just merge in the changes, so I went through and manually copied over the interim commits you made.

Major changes: 
* most of the pages now center vertically and then expand from the center. I find that this is best across the whole experiment in terms of consistency and readability.
* new brand colors that follow the same general theme from before, but now have sharper contrast
* consistent fonts that scale well (Kreon gets a little clippy at larger sizes)
* changed most of the Javascript to target IDs and not classes. I'll fix the rest of the JS as my next run through

I could walk you through everything specifically, but I think it speaks for itself if you just run through a couple of the demo trials.