.optional-mark::after {
    content: "任意";
    background-color: #575152;
    color: #fff;
    font-size: 12px;
    font-weight: bold;
    min-width: 10px;
    padding: 3px 7px;
    margin: 0px 5px;
    line-height: 1;
    vertical-align: middle;
    white-space: nowrap;
    text-align: center;
    border-radius: 10px;
    display: inline-block;
}