Add announcement alert
Add a new kind of alert to style any announcements differently. This is for gitlab-com/marketing&234 (closed).
Documentation: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30734
Review app: http://announcement-alert.178.62.207.141.xip.io/ce/development/documentation/styleguide.html#announcement
Edited by Marcia Ramos