CMS CSS Minor Polishing Tweaks

Fixed what I believe to be a few very minor CSS regressions, that appeared after the CSS restructure for the side-by-side preview.

- Reverted background of the right panel (and tab active state) to the slightly darker shade (as per 3.0) to keep each of the 3 panels visually separate.

- Slightly increased padding on ui-tabs-panel as felt a but too close for comfort. Had decreased since 3.0.

- Decreased padding for logged in user name in menu, felt too excessive. (3.0 was neater)

- Evened out padding above buttons in site tree sidebar (as 3 was)

Screenshots showing changes:
3.0: http://spdr.me/xauh
3.1 before commit: http://spdr.me/jkIe
3.1 after commit: http://spdr.me/IxtB

![3 1-after](https://f.cloud.github.com/assets/329880/251567/1a7d8c02-8b6a-11e2-9300-311bc902574a.png)