Reduces padding of the Overview shelf in no button mode.

Before: https://screenshot.googleplex.com/iw6baTCfoy2.png
After: https://screenshot.googleplex.com/8CcsQvLhYDo.png
Desired: https://b.corp.google.com/action/issues/139551306/attachments/26925873?download=false

Test: Examined before and after padding and verified 3-button is unaffected.
Fixes: 139551306

Change-Id: Ia416399cf25e7c6c2fb8aa84ad20e7ad74dcd31b