Stylesheet rules for structural scenes. Class-scoped: inert when
no structural elements exist, so they merge unconditionally.
Literal colors for the same reason COMPOUND_CONTAINER_RULE uses
them (Cytoscape cannot read CSS variables; theme-resolved values
ride through ThemeManager for hosts that merge the derivation).
Stylesheet rules for structural scenes. Class-scoped: inert when no structural elements exist, so they merge unconditionally. Literal colors for the same reason COMPOUND_CONTAINER_RULE uses them (Cytoscape cannot read CSS variables; theme-resolved values ride through ThemeManager for hosts that merge the derivation).