Revert Hovercard CSS changes

Summary: Fixes T8094, I'll just wait for a 'improve hovercards' round of changes during the redesign

Test Plan: Test UIExamples

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8094

Differential Revision: https://secure.phabricator.com/D12737