Resolve "Landing page displays improperly on 768p screen"

Closes #933 (closed)

This ensure the password input doesn't overflow outside of the container (as shown in #933 (closed)). As for the really narrow layout, I have no easy fix right now, but the work done in !923 (merged) will reduce the sidebar width and leave more room to content, so it should make the issue less proeminent :)

cc @funkwhale/reviewers-front