Theme families to expand with the additional derived properties
If provided, themes from this family are used to fill in missing
cssVariables
in the theme definitions to make sure each theme definition has all necessary
cssVariables
The expanded theme families
Add the derived properties in ThemeDefinitionExpanded to ThemeDefinitions in the given ThemeFamiliesById and fill in any missing
cssVariables
in the theme definitions with those from the default themes.Does not modify the input object.