css画空心箭头

<i class="u-arrow u-arrow-left "></i>

.u-arrow {        display: inline-block;        width: 7px;        height: 7px;        border-top: 1px solid #999;        border-right: 1px solid #999;    }    .u-arrow-up {        transform: rotate(-45deg);    }    .u-arrow-down {        transform: rotate(135deg);    }    .u-arrow-left {        transform: rotate(-135deg);    }    .u-arrow-right {        transform: rotate(45deg);    }