- careful with font-size in collapsed so that the collapsor doesn't
  change sizes
- pull some padding off the top of the thread

fixes #45

Fixes #21.

Fixes #16.

Add background back, along with a box shadow, for that nice
Twitter-like blur out of the covered text.

Keep broad resets namespaced and out of common.scss.

It's necessary to bring the heatmap back inside the margins so that
it's visible, which requires some retooling of z stacking to get event
bubbling to behave.