Runtime support for the wrappers the Kit generates — pure assigns (map) manipulation, so a wrapper stays a thin delegator to the real component. One transform/2 handles both worlds:

• styled (spec.attrs) — remap a customized color/variant/size value to the component's neutral base, then layer your classes (verbatim — write the ! yourself so they win without a class-merge, since the generated components don't run one), preserving the attr's type;
• headless (spec.class) — add your part classes (verbatim [&_[data-part=…]]:) to the root.