fixing d-dropdown heading overlap

as discussed here: https://meta.discourse.org/t/small-ui-bug-show-more-overlap-with-reuslt-list-in-search-box/17194

![screenshot 2014-07-04 02 20 06](https://cloud.githubusercontent.com/assets/1681963/3478798/4c2bfa6a-0344-11e4-811f-f4550983e19b.png)