New layout

Hey T...

The new layout is a work in progress. Changing some DOM elements caused a few things to break in the JS.

If you have a chance on Monday or Tuesday, can you look at any of the following?

- Fixing the way-finding header in the site sub-head
- Moving the definitions header
- Toggling an active class on .main-content (currently this only toggle elements in the header)

As I get further into the layout/responsiveness I can look at fixing these things too, but figured I'd ask for help if possible.

Thanks!