vant/build/utils/postcss_pipe.js

var config = {
    'bem': {
        'shortcuts': {'component': 'b', 'modifier': 'm', 'descendent': 'e'},
        'separators': {'descendent': '__', 'modifier': '--'}
    }
};
var reset = require('postcss-css-reset')();

// https://github.com/trysound/postcss-easy-import
var partialImport = require('postcss-easy-import')();

// 这不是bem，虽然名字叫bem，其实它是suit
// https://github.com/saladcss/saladcss-bem
var bem = require('saladcss-bem')(config.bem);

// https://github.com/jonathantneal/precss
var precss = require('precss')();

// https://github.com/postcss/autoprefixer
var autoprefixer = require('autoprefixer')();

module.exports = function (webpack) {
  // 顺序很重要
  return [
    partialImport,
    bem,
    precss,
    autoprefixer,
    reset
  ];
};