CSS小功能实现

#prev {
    display: block;
    width: 0;
    height: 0;
    border-bottom: 7px solid #4d4d4f;
    border-right: 10px solid transparent;
    border-left: 10px solid transparent;
    margin: 0 auto;
}

#next {
    display: block;
    width: 0;
    height: 0;
    border-top: 7px solid #4d4d4f;
    border-right: 10px solid transparent;
    border-left: 10px solid transparent;
    margin: 0 auto;
}