Svelte/Sapper `:global` prefixer for Less

global-styles.js

export default {
  install (less, mgr) {
    mgr.addPostProcessor({
      process (input, meta) {
        return input.replace(/:global (.*?)\s*([{,])/g, ':global($1)$2');
      }
    });
  }
}

rollup.config.js

// ...
import { less } from 'svelte-preprocess-less'
import globalStyles from './global-styles'

const preprocess = {
  style: less({ plugins: [globalStyles] })
};

export default {
  client: {
    // ...
    plugins: [
      svelte({
        // ...
        preprocess
      })
    ]
  },
  server: {
    // ...
    plugins: [
      svelte({
        // ...
        preprocess
      })
    ]
  }
}