I'm guessing that if you set ElementFont = efCSS then it uses ElementClassName, and if you set it to efProperty then it should use the values in the Font Property.
If this is true, then efProperty isn't working correctly.
In particular, I've got some TWebMemo's and I set Font.Name = Courier New, .Size = 10, and they have no effect (the ParentFont has Size=12).
The fonts are the parent's even though the ParentFont property is UN-checked.
Even in TWebLabels this does nothing.
Sometimes I want to shrink down the font size a couple of points, and I'm not sure how to do that with CSS. (CSS is something that has never made much sense to me because it has a flat namespace where things get inherited invisibly, while I tend to think of things hierarchically using a nested namespace.)
I don't know enough about CSS or how to wade through the hundreds of options for ElementClassName to find what I want quickly, so it's a lot easier to just set things in the Font using the Object Inspector for now and pretty things up later.
