[web] [fix] regression: chat tabs disabled lost its bottom border when changing global border color.

Summary:

disabled state should match figma

Currently master looks like this:

Regression was added here: https://github.com/CommE2E/comm/commit/b64048cb2096a5c96c52212a16f0f125f581b31e

Test Plan: check figma: https://www.figma.com/file/a1nkbWgbgjRlrOY9LVurTz/?node-id=1170%3A77104 that the design looks correct. Toggle background and focused

Reviewers: atul, palys-swm

Reviewed By: palys-swm

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

Differential Revision: https://phabricator.ashoat.com/D3317