Remove button-secondary class from Collapse link in theme installer; unify Collapse button styles in theme installer and Customize screen; add a border around the Collapse icon so it remains visible on dark backgrounds; move the color styles to colors-fresh. Fixes #26230.
Built from https://develop.svn.wordpress.org/trunk@26389


git-svn-id: http://core.svn.wordpress.org/trunk@26289 1a063a9b-81f0-0310-95a4-ce76da25c4cd