[web] Fix Safari layout after D893

Summary: I accidentally broke Safari in D893. This diff fixes it, and makes sure Chrome and Firefox are still fixed too.

Test Plan: Test scrolling up in chat view in Safari, Chrome, Firefox

Reviewers: atul, palys-swm

Reviewed By: atul

Subscribers: KatPo, zrebcu411, Adrian, subnub

Differential Revision: https://phabricator.ashoat.com/D898