1. 扩展点击区域

extend-click()
    position: relative
    &:after
        content: ''
        position: absolute
        top: -10px
        left: -10px
        right: -10px
        bottom: -10px
// 或者给&:before加

2. 响应式图片

bg-image($url)
    background-image: url($url + "@2x.png")
    @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
        background-image: url($url + "@3x.png")