[Redesign] Add clear:both to standard-page

Summary: Ref T8099, Ref T8614. Some users I guess scale Phabricator up 150%, this adds additional clearing.

Test Plan: Scale pages up.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8099, T8614

Differential Revision: https://secure.phabricator.com/D13530