Element-scoped overrides

const overflow = new Overflow('live_pub_...', {
  appearance: {
    size: 'normal',
    variables: { colorPrimary: '#3b82f6' },
  },
});

// Inherits the instance theme verbatim.
overflow.card().mount('#card');

// Overrides size and one token; still inherits colorPrimary.
overflow.bank({
  appearance: {
    size: 'compact',
    variables: { inputBorderRadius: '0px' },
  },
}).mount('#bank');

overflow.card({
  appearance: {
    variables: { inputHeight: '48px' },
  },
}).mount('#card');

// Card renders with inputHeight: '48px' AND colorPrimary from the instance.

card.update({ appearance: { variables: { inputHeight: '48px' } } });

overflow.checkout({
  paymentMethods: ['card', 'bank'],
  card: {
    appearance: { variables: { colorPrimary: '#f00' } }, // Type error
  },
});