UITheme.h file
UITheme: the engine's theme.
One style sheet (Trinyx/assets/ui/trinyx.ggss): the engine's colours as tokens, layered over the built-in sheet so the built-in widgets use them, plus the styles of the engine's own tools. A game that wants the engine look applies it; a game with its own look layers its own sheet on top, or leaves the theme out.
GGUI::StyleTable styles; UITheme::Apply(styles); // the built-in sheet, with the theme over it styles.SetSheet("game", ...); // the game's own, over both UITheme::Watch(host, styles); // development: hot reload the theme's file
The sheet is compiled in, so it works without the file.