如何修改vant dialog title 的样式

<van-dialog v-model="dateTimePickerShow" show-cancel-button>
      <slot name="title"><span style="margin:30px;height:20px;display:block;font-size:17px">选择时间:<span style="color:blue;padding-left:5px">{{ datepickerTitle }}</span></span></slot>
      <van-divider />
      <van-datetime-picker
        v-model="currentDate"
        :show-toolbar="false"
        type="datetime"
      />
    </van-dialog>