【移动端适配】适配1个像素的border

.b-top,.b-btm {
    position:relative;
}
    .b-top:before {
        content:' ';
        display:block;
        width:100%;
        position:absolute;
        left:0;
        top:0;
        border-top:1px solid #e7e7e7;
        -webkit-transform-origin:left top;
    }
    .b-btm:after {
        content:' ';
        display:block;
        width:100%;
        position:absolute;
        left:0;
        bottom:0;
        border-bottom:1px solid #e7e7e7;
        -webkit-transform-origin:left bottom;
    }

    /* Retina 适配 */

@media only screen and (-webkit-min-device-pixel-ratio: 2.0),
only screen and (min--moz-device-pixel-ratio: 2.0),
only screen and (-o-min-device-pixel-ratio: 200/100),
only screen and (min-device-pixel-ratio: 2.0) {
    .b-top:before,.b-btm:after {
        -webkit-transform: scaleY(0.5);
        transform: scaleY(0.5);
    }
}

/* 三倍屏 适配 */

@media only screen and (-webkit-min-device-pixel-ratio: 2.5),
only screen and (min--moz-device-pixel-ratio: 2.5),
only screen and (-o-min-device-pixel-ratio: 250/100),
only screen and (min-device-pixel-ratio: 2.5) {
   .b-top:before,.b-btm:after{
        -webkit-transform: scaleY(0.33333334);
        transform: scaleY(0.33333334);
    }
}