Global Notification Bar

I’m considering using Ghost for my next project, but have a few questions about capabilities before I decide.

Is it possible to add a global notification bar at the top of the site that users could toggle on/off from the Ghost admin? I understand it could be added with code in the theme template, but I’m not seeing a way to make it accessible to users/writers in the admin.

What’s the best way to approach something like this?

Once the code is added to the theme, I would suggest using CSS in Ghost Admin Code Injection settings to hide it, for example:

  . notification-bar { display: none; }