R1:638a9471fdea

Crisp CSS rules for JX.Tooltip

Summary: Ref T12174. More white and bolder. So crisp

Test Plan: Hover.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12174

Differential Revision: https://secure.phabricator.com/D17286