vant/packages/vant-cli/src/compiler/compile-css.ts

import postcss from 'postcss';
import postcssrc from 'postcss-load-config';
import { transform } from 'esbuild';
import { POSTCSS_CONFIG_FILE } from '../common/constant.js';

export async function compileCss(source: string | Buffer) {
  const config = await postcssrc({}, POSTCSS_CONFIG_FILE);
  const { css } = await postcss(config.plugins as any).process(source, {
    from: undefined,
  });
  const result = await transform(css, {
    loader: 'css',
    minify: true,
    target: ['chrome53', 'safari10'],
  });
  return result.code;
}