Thanks Brian and John---one question leads to another:
This small modification with a FontSize option for the Cell works:
newNB = CreateWindow[{}]
NotebookWrite[newNB,
Cell[BoxData[MakeBoxes[Module[{x, y, z}, z = x y; Sin[z]]]], "Input",
Background -> GrayLevel[0.95],
FontSize -> 24]]
But, I am curious why the FontSize option is not working in this:
CreateDialog[
Cell[BoxData[MakeBoxes[Module[{x, y, z}, z = x y; Sin[z]]]], "Input",
Background -> Lighter@Pink, FontSize -> 24]]
CreateDialog returns a NotebookObject, but NotebookWrite doesn't. However, I would have thought that CreateDialog creates a NotebookObject with the specified Cell and then returns the NotebookObject that it created.
I couldn't get this to work on John's version as well.
Addendum: After a bit of digging (i.e., saving the Dialog and looking inside the file.nb) , I see that the Dialog has the delayed rule option: FontSize:>CurrentValue["PanelFontSize"]...
The documentation seems to imply that this would work:
CurrentValue["PanelFontSize"] = 24
But, CurrentValue is apparently Protected; so I tried this:Unprotect[CurrentValue]
CurrentValue["PanelFontSize"] = 24
But, it didn't have any effect on the Dialog window.
