rem

// 设计稿宽度 : 750  ( 2倍图 )
// 缩放比例 : 100   ( 1rem === 100px )
    (function (win, doc) {
      function setRootFontSize() {
        let docWidth = doc.documentElement.getBoundingClientRect().width

        doc.documentElement.style.fontSize = docWidth / 750 * 100 + 'px'
      }
      setRootFontSize()
      win.addEventListener('resize', setRootFontSize, !1)
    })(window, document)