Miscellaneous cleanup

# Changes
 - Add [dark background](https://cloud.githubusercontent.com/assets/583202/4670125/45c82702-5574-11e4-9242-cf4fb41b537a.png) for patterns that were unreadable without it.
 - Adds anchors to style guide modifiers for specific style overrides (see above), or for linking directly to a modifier.
 - Change focus state for buttons to be more noticeable.
 - Fixes visual bug where clicking on a disabled button would show darker text color.