doc links

- Add background pattern
- Shared center wrapper for top and main
- Smaller top
- Drop shadow
- Increased margin for main page logo

Whenever the CSS changes, it's fingerprint (i.e., filename) should
change. This way the file can be cached forever.

* Background color
* Synced code block background colors
* Heading and paragraph margins to make them appear closer to each other
* Padding for main content