Clean up some search result alignment CSS

Summary: Aligns the search result list to the right of the input box, adds a little space, removes a double border.

Test Plan: Search on desktop, mobile, tablet breakpoints. Double check normal typeahead results.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17345