Another option is to, instead of having the Role "RolePage" with two attributes, have two required methods "textFont" and "textSize". You could then have a PageDefault role that is equivalent to your current RolePage role.

CairoPage could then compose the role "RolePage" and implement its own textFont and textSize accessors that delegate to the cairoFont attribute.

Other page classes could just compose PageDefault instead of RolePage.