Specify body colours on demo pages

Specifies the color & background-color on the demo pages.

Feel free to discard, noticed they were undefined when using [ish](http://bradfrost.com/demo/ish/?url=http%3A%2F%2Ffilamentgroup.github.io%2Ftablesaw%2Fdemo%2Fswipe.html#100) and it got to me.