[web] [refactor] chat thread list item menu html cleanup

Summary:
fix up html + css while changing the unread theme

before:

Test Plan: click unread, no new functionality or changes should happen.

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3180