Fix 1px button cut off on topic progress up / down buttons.

This fixes an incredibly minor issue with the up / down buttons being cut off by 1px on Chrome & Safari.

![Screen Shot 2013-02-11 at 12 02 10](https://f.cloud.github.com/assets/822528/144923/74e31b7c-7444-11e2-8d1a-c85f24c27de6.png)