Updated admin styles for ad hoc options.

This change updates the look of the flexi variants area a little.  It matches the 1.3 style a little better.  A quick sample:

Before:
![flexi-variants-style-before](https://f.cloud.github.com/assets/764390/498405/cbbf85da-bc14-11e2-8ffa-8ecbf7eee559.png)

After:
![flexi-variants-after](https://f.cloud.github.com/assets/764390/498406/d06fedcc-bc14-11e2-824a-cf5a93aee359.png)