blog-tagged-template-5.js

function styled(css, ...variables) {
  // . . .
  const computedCss = css
    .map(
      (chunk, index) =>
        // now fires a callback at 'variables[index]'
        `${chunk}${variables[index] ? variables[index](props) : ''}`
    )
    .join('')
  return computedCss
}

const Button = styled`
  /* now passes a callback that accepts a 'props' object */
  background: ${({ primary, theme }) =>
    primary ? theme.colors.primary : theme.colors.secondary};
    /* ... */