Stylizing GtkNotebook Tabs in Theme (gtkrc)

[Kevin]

I don't see anything that would create the highlight at the top of the tab without using images, or using an engine that is built to do that.

The GTK code I've looked at just draws six lines when it's drawing an extension and makes no allowance for anything other than the content (label and or icon) and the curvature/focus-line-width/xthickness/ythickness padding.