Customize CSS Class In React-Bootstrap Under CSS-Modules

For a quick start, I used electron-react-boilerplate as the basis for developing my tiny smart-todo app, which however brought me some trouble with css class names.

  1. css won’t work when assigning class names of string type directly to ‘className’ prop of the react component.
  2. css won’t work when customizing css class of the children inside the react component.

After a hard search and try, I found the reason and solution.

First I will introduce some concept and packages.

1. css in react

There are basically 2 ways to style in react components:

  1. regular css stylesheets

    By importing css stylesheets files, we can pass a string as the className prop of a component.

    Class names can be multiple. There’s an effective package classnames for conditionally joining classNames together.

  2. inline styles

    We can pass a js object as the style prop of the component.

2. css-modules

A css module is a CSS file in which all class names and animation names are scoped locally by default. It added additional naming strategies to the class names, which can also customized by developers themselves.

/* home.css */
.container {
.mainSection {
.toolSection {
import styles from './home.css'

<div className={styles.container}>
  <div className={styles.mainSection}><MainSection/></div>
  <div className={styles.toolSection}><ToolSection/></div>

In webpack config, the naming strategy can be customized:

  test: /^((?!\.global).)*\.css$/,
  use: [
      loader: 'style-loader'
      loader: 'css-loader',
      options: {
        modules: true,
        sourceMap: true,
        importLoaders: 1,
        localIdentName: '[name]__[local]__[hash:base64:5]',

It also provide a way to speicify global and local to the selectors in a css module.

:global(.globalclassname) {
:local(.localclassname) {

If global specified, the selector is scoped globally, whose identifier name will not be changed by the naming strategy.

3. react-css-modules

By introducing css-modules, there are some annoy limitations for styling components. This is a convinient utility to make up for the disadvantages.

I used the light package called babel-plugin-react-css-modules, as it has a lot smaller performance overhead and fullfills my requirements.

I can modify the example above as follows:

import './home.css'

<div styleName='container'>
  <div styleName='mainSection'><MainSection/></div>
  <div styleName='toolSection'><ToolSection/></div>

Attention here! See How does it work.

The styleName will be parsed to the className finally. If the result className doesn’t meet the rules of the css-modules naming strategy, the right css style will not be found. So a configuration in .babelrc is required:

"plugins": [
  ["react-css-modules", {

The value of generateScopedName should be the same as that of localIdentName decribed above.

Solutions to the 2 Questions

  1. In electron-react-boilerplate, it uses css-modules. So all selectors defined in *.css files are locally scoped and changed by name, whereby the string value directly passed to the className don’t match the changed selector’s name.

    We should use className={styles.classname}, or we can ask react-css-module for help.

  2. The child component of a react component sometimes is classNamed with a globally scoped class (see some source code examples in react-bootstrap. If we want to override the styles, we can’t specify the selector’s name directly in a css module because it is locally scoped and will be changed name.

    We should use :global(.classname) instead.

Analogy between css and shader

As before I wrote some shaders for Unity games, it is seemly same annoying to write css styles. They are both used to define the looks of elements to render. They are both difficult to debug like scripts. Maybe most of fresh developers waste lots of time in try. But after working out a friendly style, it is considerably satified. How do you think?