Style text boxes and tab panels in dashboards

Summary: Adds basic borders, spacing to tab panels and text boxes.

Test Plan:
Added some of each to my Dashboard.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5078

Differential Revision: https://secure.phabricator.com/D9216