::after

a::after {
  content: " (" attr(href) ")";
}

.dead-link {
  text-decoration: line-through;
}

.dead-link::after {
  content: url("/shared-assets/images/examples/warning.svg");
  display: inline-block;
  width: 12px;
  height: 12px;
}

<p>
  The sailfish is named for its sail-like dorsal fin and is widely considered
  the fastest fish in the ocean.
  <a href="https://en.wikipedia.org/wiki/Sailfish"
    >You can read more about it here</a
  >.
</p>

<p>
  The red lionfish is a predatory scorpionfish that lives on coral reefs of the
  Indo-Pacific Ocean and more recently in the western Atlantic.
  <a href="" class="dead-link">You can read more about it here</a>.
</p>

::after {
  content: /* 值 */;
  /* 其他属性 */
}

<p class="boring-text">这是些无聊的文字</p>
<p>这是不无聊也不有趣的文字</p>
<p class="exciting-text">在 MDN 上做贡献简单又轻松！</p>

.exciting-text::after {
  content: "<- 让人兴兴兴奋！";
  color: green;
}

.boring-text::after {
  content: "<- 无聊！";
  color: red;
}

<span class="ribbon">看看这段文字后的橙色盒子。</span>

.ribbon {
  background-color: #5bc8f7;
}

.ribbon::after {
  content: "这是一个漂亮的橙色盒子。";
  background-color: #ffba10;
  border-color: black;
  border-style: dotted;
}

<p>
  这里我们有包含了一些<span tabindex="0" data-descr="鼠标悬停时出现的小弹出窗口"
    >工具提示</span
  >的<span tabindex="0" data-descr="文字和标点符号的集合">文字</span>。
</p>

span[data-descr] {
  position: relative;
  text-decoration: underline;
  color: #00f;
  cursor: help;
}

span[data-descr]:hover::after,
span[data-descr]:focus::after {
  content: attr(data-descr);
  position: absolute;
  left: 0;
  top: 24px;
  min-width: 200px;
  border: 1px #aaaaaa solid;
  border-radius: 10px;
  background-color: #ffffcc;
  padding: 12px;
  color: #000000;
  font-size: 14px;
  z-index: 1;
}