R1:8fb227d35202

Update Remarkup Note Styles

Summary: Update notes, important, and warnings to look different than codeblocks.

Test Plan: test in diviner and legalpad

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin, chad, avivey

Differential Revision: https://secure.phabricator.com/D8592