按需加載得先在 babel.config.js 中配置

module.exports = {
  plugins: [
    [
      'import',
      {
        libraryName: 'vant',
        libraryDirectory: 'es',
        // 指定樣式路徑
        style: name => `${name}/style/less`
      },
      'vant'
    ]
  ]
};

然后再配置主題色

 loaderOptions: {
          less: {
              modifyVars: {
                red: '#03a9f4',
                blue: '#3eaf7c',
                orange: '#f08d49',
                'text-color': '#111',
                'active-color': '#B4E7A0',
              }
            }
        }