fix styling on toolbar buttons in newfiles

Change-Id: I0e7d01afb627b3bd7c26aafc63dbb2559ef4f67b
Reviewed-on: https://gerrit.instructure.com/41704
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Dan Minkevitch <dminkevitch@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>