Theming without duplication

Dark mode built by copying every component and editing colors by hand is how you get two systems that drift apart by Friday.

The payoff of the whole model: components stay fixed. Only token values change per theme. Light, dark, and brand are alternate value sets over the same structure.

Same names. Same hops. button-bg still points at primary. primary still points at blue-600. The hex behind blue-600 is what moves.

A copied dark mode on the left — leftover light hexes. Same hops on the right, new primitive values.

The card, the input, and the button did not get rewritten. They resolved a different value set. That is a theme.