`:hover::before` 的目的是什么？

Question

我正在查看 html + css 按钮，但我很困惑为什么 before 伪元素与 hover 伪元素一起使用 class。

.anchor-style {
  font-size: 18px;
  letter-spacing: 2px;
  text-transform: uppercase;
  display: inline-block;
  text-align: center;
  width: 270px;
  font-weight: bold;
  padding: 14px 0px;
  border: 3px solid #ff0072;
  border-radius: 2px;
  position: relative;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.16), 0 3px 6px rgba(0, 0, 0, 0.1);
}

.anchor-style::before {
  -webkit-transition: 0.5s all ease;
  transition: 0.5s all ease;
  position: absolute;
  top: 0;
  left: 50%;
  right: 50%;
  bottom: 0;
  opacity: 0;
  content: '';
  background-color: #ff0072;
  z-index: -2;
}

.anchor-style:hover::before {
  -webkit-transition: 0.5s all ease;
  transition: 0.5s all ease;
  left: 0;
  right: 0;
  opacity: 1;
}

<a class="anchor-style" target="_blank" href="http://www.infinity2o.com">
    Say Hi to My New Matches
</a>

锚标签上已经有常规样式，为什么还需要使用 before 伪元素进行更多样式设置？

我试着查看之前的伪元素文档，了解到它对于在每个 p 标签之前添加元素很有用...但我不明白它对按钮的解释有何不同。

Answer 1

动画效果。 ::before的使用也是cleaner.

The ::before selector inserts something before the content of each selected element(s).

所以你可以把::before伪想成一个空的div。以下等效于没有 ::before 伪

.anchor-style {
  font-size: 18px;
  letter-spacing: 2px;
  text-transform: uppercase;
  display: inline-block;
  text-align: center;
  width: 270px;
  font-weight: bold;
  padding: 14px 0px;
  border: 3px solid #ff0072;
  border-radius: 2px;
  position: relative;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.16), 0 3px 6px rgba(0, 0, 0, 0.1);
}

.before {
  -webkit-transition: 0.5s all ease;
  transition: 0.5s all ease;
  position: absolute;
  top: 0;
  left: 50%;
  right: 50%;
  bottom: 0;
  opacity: 0;
  content: '';
  background-color: #ff0072;
  z-index: -2;
}

.anchor-style:hover > .before {
  -webkit-transition: 0.5s all ease;
  transition: 0.5s all ease;
  left: 0;
  right: 0;
  opacity: 1;
}

<a class="anchor-style" target="_blank" href="http://www.infinity2o.com">
    <div class="before"></div>
    Say Hi to My New Matches
</a>

`:hover::before` 的目的是什么？

What's the purpose of `:hover::before`?

html

css

hover

pseudo-class

pseudo-element