目标效果：

缩小浏览器之后

在最前面引入flexible.js

。。。

。。

flexible.js 内容如下

(function flexible (window, document) {
var docEl = document.documentElement
var dpr = window.devicePixelRatio || 1
// adjust body font size
// console.log(dpr)
function setBodyFontSize () {
if (document.body) {
document.body.style.fontSize = (12 * dpr) + 'px'
}
else {
document.addEventListener('DOMContentLoaded', setBodyFontSize)
}
}
setBodyFontSize();

// set 1rem = viewWidth / 10  
function setRemUnit () {  
    var rem = docEl.clientWidth / 10  
    docEl.style.fontSize = rem + 'px'  
}

setRemUnit()

// reset rem unit on page resize  
window.addEventListener('resize', setRemUnit)  
window.addEventListener('pageshow', function (e) {  
    if (e.persisted) {  
        setRemUnit()  
    }  
})

// detect 0.5px supports  
if (dpr >= 2) {  
    var fakeBody = document.createElement('body')  
    var testElement = document.createElement('div')  
    testElement.style.border = '.5px solid transparent'  
    fakeBody.appendChild(testElement)  
    docEl.appendChild(fakeBody)  
    if (testElement.offsetHeight === 1) {  
        docEl.classList.add('hairlines')  
    }  
    docEl.removeChild(fakeBody)  
}  

}(window, document))

然后根据当前浏览器宽度: 2048px = 10rem 推导出204.8px = 1rem 。对所有标签宽高，字体用到px的地方，换算成rem即可

> screen.width
< 2048