It will become a child of Tabula Rasa when it's patched, but it shouldn't be yet! Make a layout layer that is a child of Core 2. Paste the entire layout layer code into that (the current layout code includes a /copy/ of Tabula Rasa for Lists to sit on top of). Then make a theme layer that is a child of your very own Lists and paste one of the theme layers' code into that.

Default font size can be changed in the Customize area, though I forget if it's under Text or Presentation.