Can't Edit Pages - You Are Offline

This must be documented somewhere or someone has run across it. Log into GRAV admin and want to edit a page. It doesn’t matter which page. I get a giant “G - GRAV” icon and a message that says “You Are Offline”. This is definitely running on a server and I’m definitely logged in.

Any ideas?

@bmcwilliams: Can you check, if your stylesheets are loaded properly? The “offline” message is something I can also see on my live-site, when I disable stylesheets.