.remMixin() {
    @functions: ~`(function() {
      var clientWidth = '1920px';
      function convert(size) {
        return typeof size === 'string' ? 
          +size.replace('px', '') : size;
      }
      this.rem = function(size) {
        return convert(size) / convert(clientWidth)*100  + 'rem';
      }
    })()`;
  }
  .remMixin();