虽然 iOS 下可以使用 0.5px 边框,但是不能兼容安卓设备。这里采用 transform 来实现

.list {list-style: none; margin:1em 0; padding:0; font-size: 14px;}
.list li {border-bottom:1px solid #999; line-height: 1.5; padding:.5em;}

@media (-webkit-min-device-pixel-ratio: 2) {
    .list li {border: 0; position:relative;}
    .list li:first-child:before {
        content: ''; position: absolute; top:0; left:0;
        width:100%; height:1px;
        background: #999;
        -webkit-transform: scale(1, 0.5);
        transform: scale(1, 0.5);
        -webkit-transform-origin: top;
        transform-origin: top;
    }
    .list li:after {
        content: ''; position: absolute; bottom:0; left:0;
        width:100%; height:1px;
        background: #999;
        -webkit-transform: scale(1, 0.5);
        transform: scale(1, 0.5);
        -webkit-transform-origin: bottom;
        transform-origin: bottom;
    }
}