Twenty Fifteen: add styles for multisite registration forms.

Props valendesigns, fixes #30776.

git-svn-id: https://develop.svn.wordpress.org/trunk@30995 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: pinking shears.


git-svn-id: https://develop.svn.wordpress.org/trunk@30996 602fd350-edb4-49c9-b593-d223f7449a82