Requirements for new 'official' style layers?

[momijizukamori]

Okay, so I've looked through the wiki and through the style comms I've found, and I haven't managed to find a nice clear set of guidelines for this. I'm interested in getting started on designing some new styles for submission as official ones, but before I get too deep into CSS, I want to make sure the layout conforms to the basic standards for official styles. So far I've discovered that 1) it has to have 1em as the base font size and 2) must be fluid-width. Are there any others? I'm probably mostly going to be working off of Tabula Rasa and it's descendants, if it matters.