content: "";
    display: inline-block;
    width: 0.22rem;
    height: 0.22rem;
    position: absolute;
    top: 50%;
    right: 0.4rem;
    border-top: 2px solid #212121;
    border-right: 2px solid #212121;
    -webkit-transform: rotate(45deg) translateY(-50%);
    transform: rotate(45deg) translateY(-50%);

记得将该元素加上定位