Improve carousel example

I tried using the carousel example's CSS from the 2.3.x branch for a project and noticed that it didn't work well on pages without a carousel. This keeps the carousel example working the same and lets the floating navbar be used on pages without carousels.

**Specificity change:**

The specificity change was specific to the 3.x branch. Slides were not the height of the container: 
![screen shot 2013-07-13 at 12 45 49 pm](https://f.cloud.github.com/assets/29612/793300/e553ab64-ebf5-11e2-8a1e-525b946d88d3.png)

Matching specificity fixed it:
![screen shot 2013-07-13 at 12 45 13 pm](https://f.cloud.github.com/assets/29612/793303/f7a98e32-ebf5-11e2-8ee9-abec1c10df40.png)

**Navbar change:**

Hiding the carousel shows these styles don't work well without a carousel:
![screen shot 2013-07-13 at 12 48 51 pm](https://f.cloud.github.com/assets/29612/793306/10708f1a-ebf6-11e2-8715-5f693e216634.png)

Letting the navbar flow and moving the negative margin means the carousel still works, and the styles can be used on carousel-free pages:
![screen shot 2013-07-13 at 12 47 04 pm](https://f.cloud.github.com/assets/29612/793307/24a01708-ebf6-11e2-94e3-b52ef7483c7a.png)