<div class="box">文字內容</div>
.box {
  background-color: #aaa;
}

.box:before {
  content: '我是 before';
  display: block;
  width: 100px;
  height: 100px;
  background-color: red;
}

.box:after {
  content: '我是 after';
  display: block;
  width: 100px;
  height: 100px;
  background-color: red;
}

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External JavaScript

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