@layer base {
  h1 {
    font-size: theme("fontSize.2xl");
  }
  h2 {
    font-size: theme("fontSize.xl");
  }
}

@layer components {
  .card {
    background-color: theme("colors.white");
    border-radius: theme("borderRadius.lg");
    padding: theme("spacing.6");
    box-shadow: theme("boxShadow.xl");
  }
}

@layer utilities {
  .content-auto {
    content-visibility: "auto";
  }
}
/* this will be abandoned unless you set the `outSideLayerCss` option */
.btn{
  background: #ffffff;
}

const _plugin = require('tailwindcss/plugin')
const returnSelfNoop = (x) => x
const css2TwPlugin = _plugin.withOptions(
  function (_options = {}) {
    const { withOptionsWalkCSSRuleObject = returnSelfNoop } = _options
    return function ({ addBase, addComponents, addUtilities, theme, addVariant, config, corePlugins, e, matchComponents, matchUtilities, matchVariant }) {
      const _baseCss = withOptionsWalkCSSRuleObject(
        {
          h1: {
            'font-size': theme('fontSize.2xl')
          },
          h2: {
            'font-size': theme('fontSize.xl')
          }
        },
        'base'
      )
      addBase(_baseCss)
      const _componentsCss = withOptionsWalkCSSRuleObject(
        {
          '.card': {
            'background-color': theme('colors.white'),
            'border-radius': theme('borderRadius.lg'),
            padding: theme('spacing.6'),
            'box-shadow': theme('boxShadow.xl')
          }
        },
        'components'
      )
      addComponents(_componentsCss)
      const _utilitiesCss = withOptionsWalkCSSRuleObject(
        {
          '.content-auto': {
            'content-visibility': '"auto"'
          }
        },
        'utilities'
      )
      addUtilities(_utilitiesCss)
    }
  },
  function (_options) {
    return {}
  }
)
module.exports = css2TwPlugin

<npm / yarn / pnpm> i -D css-to-tailwindcss-plugin

<npm / yarn / pnpm> i -D tailwindcss sass

css2plugin build path/to/your.css path/to/your-another.scss --out ./tw-plugins

import { createContext } from 'css-to-tailwindcss-plugin'

const ctx = createContext({
  // pass options to postcss-import
  atImportOptions: {},
  // pass to sass options
  sassOptions: {},
  // tailwind.config.js path `string` or tailwind Config
  tailwindcssConfig: '',
  // if resolve tailwindcss Functions & Directives  (like theme() and @apply etc....)
  // should be used with `tailwindcssConfig`
  tailwindcssResolved: false,
  // pass options to babel generator
  generatorOptions: {},
  // default throw all css outside @layer
  // 'base' | 'components' | 'utilities'
  outSideLayerCss: 'components',
  // generate tailwindcss plugin with `plugin` api or `plugin.withOptions` api
  withOptions: true,
  // custom handler
  interceptors: {
    css:[
    (root,ctx)=>{
      // do sth
    }
  ]},

  postcssPlugins:(plugins)=>{
    // plugins.push / splice ...
  }
})
// load css node into context map
await ctx.process('path/to/your.css')

await ctx.process('path/to/your.scss')

const code = ctx.generate() // return code then you can fs.writeFile

const path = require('node:path')

/** @type {import('tailwindcss').Config} */
module.exports = {
  // ...
  plugins: [
    require('css-to-tailwindcss-plugin/tailwindcss')({
      entries: [
        // your css entry path
        path.resolve(__dirname, './theme-multiple.css'), 
        path.resolve(__dirname, './common.scss'
      )],
      // tmp plugins cache dir, default path is `process.cwd() + node_modules/.css-to-tailwindcss-plugin`
      // cacheDir: string

      // other options same to createContext
      // ...options
      // note: `tailwindcssResolved` is invalid in `tailwindcss plugin`, because `tailwindcss` is an async postcss plugin, while `tailwindcss plugin` **MUST** be sync!
      

      // you can use this method to intercept plugin with `withOptions`
      withOptionsWalkCSSRuleObject(cssObj, layer) {
        console.log(cssObj, layer)
        // don't forget to return it
        // this will replace origin css obj so you can add prefix here!
        return cssObj
      }
    })
  ],
  // ...
}

<npm / yarn / pnpm> i -D tailwindcss

import { createContext } from 'css-to-tailwindcss-plugin'

const ctx = createContext({
  // should be set to true
  tailwindcssResolved: true,
  // tailwind.config.js path `string` or tailwind Config
  // for tailwindcss resolve (like theme() and @apply etc....)
  tailwindcssConfig: 'path/to/your/tailwind.config.js'
})