feat(theme): export z-index constants

src/atoms/Dropdown/DropdownBody.js

@@ -9,7 +9,7 @@ import { Portal } from 'react-portal';
 import { withDropdownContext } from './DropdownContext';
 import { offsetSizes, defaultTheme, DropdownBodyTag } from './DropdownBody.theme';
 import type { PropSizes } from '../../types';
-import { Z_INDEX } from '../../theme/zIndex';
+import { Z_INDEX } from '../../theme';
 
 /**
  * @prop {*} background options for background color

src/index.js

@@ -1,7 +1,7 @@
 // @flow
 
 export { ThemeProvider } from 'emotion-theming';
-export { defaultTheme, resetGlobal } from './theme';
+export { defaultTheme, resetGlobal, Z_INDEX } from './theme';
 export * from './atoms';
 export * from './molecules';
 

src/theme/index.js

@@ -2,5 +2,6 @@
 
 export { COLORS, PALETTE } from './colors';
 export { SIZES } from './sizes';
+export { Z_INDEX } from './zIndex';
 export { defaultTheme } from './defaultTheme';
 export { resetGlobal } from './resetGlobal';