[web] Fix drawer item not reaching the edge in full screen
Summary: When a chat was open, and as such highlighted in the drawer, you could see it didn't quite reach the edge. Because the browser has a border, this was not visible when not in the full screen mode.
Test Plan: Run web app and electorn app. Check that a highlited item touches the left edge of the screen.
Reviewed By: michal
Subscribers: ashoat, tomek, atul
Differential Revision: https://phab.comm.dev/D6732