小程序Vant组件怎么将默认样式单位px转为rpx

npm init //一路回车 npm install --production npm i @vant/weapp -S --production

npm install gulp gulp-postcss postcss-px2units --save-dev

var gulp = require('gulp');var postcss = require('gulp-postcss');var pxtounits =  require('postcss-px2units');gulp.task('css', function () {  return gulp.src(['miniprogram_npm/@vant/weapp/**/*.wxss'])    .pipe(postcss([pxtounits({      multiple: 2,      targetUnits: 'rpx'    })]))    .pipe(gulp.dest('miniprogram_npm/@vant/weapp/'));});

 "scripts": {    "build": "gulp css",    "test": "echo "Error: no test specified" && exit 1"  },

npm run build