Theme styles
One render theme can ship several styles.
What a style is
A style is a variant of a render theme. The dialog lists all available styles under Style. Choose one to change the appearance of the map without switching themes.
Categories
Categories toggles groups of map features on or off within the chosen style. Use categories to simplify a map — hide or show entire classes of features such as roads, paths or buildings.
Apply
The selection takes effect on the map immediately. Press Close to close the dialog.