I think of it as the spice rack. Every ingredient the system is allowed to cook with sits here, and nothing gets added anywhere else. The file is called subatomic, and it holds ninety-one core values, the spacing steps and the color ramps, and names like color.background.subtle-hover that say what those values are for. It exports from Figma as JSON, so engineering reads the same file the designs are built from.
The core values carry four modes: a default, a warm variant and two brand themes. Components only ever point at names, so a theme is another column of values. Nobody has to duplicate a component to get one.