ia.css: thinner-looking topic bubbles

Because of society's harsh standards, the topic bubbles were forced to go on a diet.

Before:
![screen shot 2014-12-15 at 1 16 40 pm](https://cloud.githubusercontent.com/assets/81969/5441222/b12e160c-845c-11e4-94ac-4ff6bbe821a7.png)

After:
![screen shot 2014-12-15 at 1 16 50 pm](https://cloud.githubusercontent.com/assets/81969/5441223/b131abbe-845c-11e4-855f-fe46d5fe5dc7.png)