Postcss plugin for esbuild with support of injecting css styles into js bundle file.
The plugin will process the styles with postcss and inject them into the out.js bundle file, so you will get a single bundle file with the styles inside.

npm i -D esbuild-postcss-inline-styles

or yarn

yarn add esbuild-postcss-inline-styles --dev

The example below shows usage plugin with tailwind and autoprefixer.
Create and configure postcss.config.js file.

// postcss.config.js

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

Create main.css file:

/** main.css **/

@tailwind base;
@tailwind components;
@tailwind utilities;

Import main.css to index.js:

// index.js

import 'main.css'

Import plugin to your esbuild.config.js

// esbuild.config.js

import * as esbuild from 'esbuild'
import postcssInlineStyles from 'esbuild-postcss-inline-styles'

await esbuild.build({
    entryPoints: ['index.js'],
    bundle: true,
    outfile: 'out.js',
    plugins: [postcssInlineStyles()],
  })

It is not necessary to pass additional parameters to the plugin, all plugins for postcss are described in postcss.config.js.