Merge branch 'wiki-css' into 'master'

Update wiki CSS

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/160779



Merged-by: Himanshu Kapoor <info@fleon.org>
Approved-by: Chad Lavimoniere <clavimoniere@gitlab.com>
Approved-by: Himanshu Kapoor <info@fleon.org>
Reviewed-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>
Co-authored-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>