Library output using css in user land and webpack library

Question

Currently, using webpack to create a library, the library contains a couple of user interfaces, these user interface components depend on the styles of the pair from the library. However, the same styles are those that are available to users so that they can access and style. What is the best way to prevent duplication of css, because I do not want user to have two copies of the style (css), if they are using extract-text-webpack-plugin, css-loader, style-loaderetc.

How to integrate styles with the webpack build UMD library?