Improve styling of post-install message area

Before: 
![before](https://f.cloud.github.com/assets/368545/1312342/ee86c456-3230-11e3-917a-c55dd77357e2.png)

After:
![after](https://f.cloud.github.com/assets/368545/1312343/f2dc6574-3230-11e3-8b40-647323a62c32.png)