Remember that you are only previewing your user CSS. It has not yet been saved!
The Mer Wiki now uses your Mer user account and password (create account on https://bugs.merproject.org/)
MediaWiki:Usercsspreview
From Mer Wiki
The Mer Wiki now uses your Mer user account and password (create account on https://bugs.merproject.org/)
Remember that you are only previewing your user CSS. It has not yet been saved!