CSS image-set()与不同尺寸背景图加载实例页面

效果：

加载的图片是？

代码：

CSS代码：

.image-set-by-zxx {
    width: 128px; height: 96px;
    background: url(./image-set-not.jpg);
    background: -webkit-image-set(url(../201410/mm-width-128px.jpg) 1x, url(../201410/mm-width-256px.jpg) 2x, url(../201410/mm-width-512px.jpg) 3x);
    background: image-set(url(../201410/mm-width-128px.jpg) 1x, url(../201410/mm-width-256px.jpg) 2x, url(../201410/mm-width-512px.jpg) 3x);
    background-size: cover;
}

HTML代码：

<h4>加载的图片是？</h4>
<div class="image-set-by-zxx"></div>