[Bug]: Compiled CSS is missing vendor prefixes, when Next.js does add them

[sawyerh]

Describe the bug

My project's CSS includes modern CSS syntax, such as the mask property. This property requires vendor prefixes (e.g. -webkit-mask) in order to properly render in Chrome.

When using the @storybook/nextjs framework, the CSS mask property is not being automatically prefixed in the processed CSS. However, Next.js does this for you, so this means the CSS shown in Storybook is somewhat broken compared to when the page is viewed

In Next.js

In Storybook

To Reproduce

1. I've created a repo with a minimum reproduction of this issue: https://github.com/sawyerh/storybook-css-prefixing-bug
2. Run the Storybook in Chrome

System

Environment Info:

  System:
    OS: macOS 13.4.1
    CPU: (8) arm64 Apple M1
  Binaries:
    Node: 18.12.1 - ~/.asdf/installs/nodejs/18.12.1/bin/node
    Yarn: 1.22.19 - ~/.asdf/installs/nodejs/18.12.1/bin/yarn
    npm: 8.19.2 - ~/.asdf/plugins/nodejs/shims/npm
  Browsers:
    Chrome: 114.0.5735.133
    Safari: 16.5.1
  npmPackages:
    @storybook/nextjs: ^7.0.24 => 7.0.24
    @storybook/react: ^7.0.24 => 7.0.24

### Additional context

_No response_

[brandon-lent]

following

[sookmax]

@sawyerh Hey, it seems like next.js uses some sophisticated postcss plugin (postcss-preset-env) to determine whether they should add vendor prefixes depending on browserslist you specified in your package.json.

Well fortunately under the hood, postcss-preset-env uses autoprefixer postcss plugin, and @storybook/nextjs's webpack is already configured to use postcss-loader when processing css files, you can manually install postcss and autoprefixer (e.g. npm install -D postcss autoprefixer) in your project and add postcss.config.js file at the project root like below:

postcss.config.js

module.exports = {
  plugins: {
    autoprefixer: {},
  },
};

postcss.config.js will be picked up and processed by postcss-loader in @storybook/nextjs, which will result in vender prefixes being automatically added to your css properties whenever you run the storybook dev server.

---

I've also added a PR to your reproduction repository (link), so see if it works correctly.

Cheers.

[sawyerh]

@sookmax Thanks for the quick response! It looks like adding the postcss.config.js does fix this in Storybook. For my project, the presence of postcss-preset-env in package.json was sufficent, and I didn't have to add autoprefixer as a direct dependency.

[ushakovfserg]

You need to be careful.
Adding postcss.config.js in project root disables default next.js internal postcss config.
According to docs it is better to set the same as internal and modify it.

I created postcss.config.js like this

const MODERN_BROWSERSLIST_TARGET = require('next/dist/shared/lib/modern-browserslist-target');

/**
 * Default configuration for PostCSS in Next.js.
 * https://nextjs.org/docs/pages/building-your-application/configuring/post-css#customizing-plugins
 *
 * Required for correct CSS in storybook, because @storybook/nextjs doesn't support it.
 */
module.exports = {
  plugins: {
    'postcss-flexbugs-fixes': {},
    'postcss-preset-env': {
      browsers: MODERN_BROWSERSLIST_TARGET,
      autoprefixer: {
        flexbox: 'no-2009',
      },
      stage: 3,
      features: {
        'custom-properties': false,
      },
    },
  },
};