If you look at the definition of a style and it says that the font
name is "+Body" or "+Headings", and the color is "Text 1" (or another
number) or "Accent 1" (or another number), then the style is
theme-aware. It means that the font face and color used by text in
theat style at any given time is determined by which theme is applied
to the document.
If the font is chosen as a specific font name, and/or the color is a
specific one, then the font and/or color won't change when a different
theme is chosen, and the style isn't theme-aware.