old_contents: export { default as List } from './components/list/';
  export { default as Button } from './components/button/';
  export { default as Flex } from './components/flex/';
  export { default as WhiteSpace } from './components/white-space/';
  export { default as WingBlank } from './components/wing-blank/';
  
new_contents: export { default as Button } from './components/button/';
  export { default as Card } from './components/card/';
  export { default as List } from './components/list/';
  export { default as Flex } from './components/flex/';
  export { default as Tag } from './components/tag/';
  export { default as WhiteSpace } from './components/white-space/';
  export { default as WingBlank } from './components/wing-blank/';
  
subject: add card & tag to index.js