"Layout may be affected by external css" is affected by Emotion

[maltenuhn]

"Layout may be affected by external css" should really only show up if there's external CSS. Emotion doesn't count.

If we can't do that because it's hard to distinguish etc, we should bring down the level of emphasis, this makes me think I've committed a grave mistake :)

[maltenuhn]

cc @alecmolloy since this might catch us out in the css className selector as well? or not?