The default style variables - the base theme's values, and the only
declaration of what variable names exist.
The module exports a single array, and holds no data of its own: families
whose members follow one template are built by loop from the variant lists
and value tables in variable_data.ts and the emitters in ramps.ts, then
spread into default_variables in place - array order is the order the CSS
renders in, so a family's spread sits where its members belong in the
cascade. What lives here is the assembly: the loop templates, the units
and calc() wrappers the tables' unitless numbers get dressed in, and the
one-off variables that belong to no family.