Css不适用于属性

Question

我尝试将图像放在div元素之前并使用此代码：

.prevent-reserve .col-7:before {
  display: block;
  position: absolute;
  right: -4px;
  top: -4px;
  width: 100px;
  height: 102px;
  color: #ffffff;
  background: url(/Content/Travelo/images/icon/prevent-reserve.png) no-repeat;
}

<a class="prevent-reserve">
  <div class="col-7">
    <label class="day-charter">
        Today
        </label>
    <label class="date-charter">1396/08/19</label>
    <span class="price-charter">2,496,000</span>
    <label>ریال</label><br>

  </div>
</a>

但不起作用。什么问题？